board/qemu/sparc64-sun4u: avoid gcc-11 warning to build the kernel

board/qemu/sparc64-sun4u: avoid gcc-11 warning to build the kernel

gcc-11 warns about what appears to be an out-of-range array access but
stop the build due to -Werror added to cflags:

arch/sparc/kernel/mdesc.c: In function 'mdesc_node_by_name':
arch/sparc/kernel/mdesc.c:647:22: error: 'strcmp' reading 1 or more bytes from a region of size 0 [-Werror=stringop-overread]
  647 |                 if (!strcmp(names + ep[ret].name_offset, name))
      |                      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
arch/sparc/kernel/mdesc.c:77:33: note: at offset 16 into source object 'mdesc' of size 16
   77 |         struct mdesc_hdr        mdesc;
      |                                 ^~~~~
arch/sparc/kernel/mdesc.c: In function 'mdesc_get_property':
arch/sparc/kernel/mdesc.c:692:22: error: 'strcmp' reading 1 or more bytes from a region of size 0 [-Werror=stringop-overread]
  692 |                 if (!strcmp(names + ep->name_offset, name)) {
      |                      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
arch/sparc/kernel/mdesc.c:77:33: note: at offset 16 into source object 'mdesc' of size 16
   77 |         struct mdesc_hdr        mdesc;
      |                                 ^~~~~
arch/sparc/kernel/mdesc.c: In function 'mdesc_next_arc':
arch/sparc/kernel/mdesc.c:719:21: error: 'strcmp' reading 1 or more bytes from a region of size 0 [-Werror=stringop-overread]
  719 |                 if (strcmp(names + ep->name_offset, arc_type))
      |                     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
arch/sparc/kernel/mdesc.c:77:33: note: at offset 16 into source object 'mdesc' of size 16
   77 |         struct mdesc_hdr        mdesc;
      |                                 ^~~~~
cc1: all warnings being treated as errors

The issue was initially reported to gcc [1] where it was analized.
As suggested, change the struct mdesc_elem * accesses from the end
of mdesc to those from the beginning of the data array.

Update the prototype of node_block(), name_block() and data_block()
since the code really seems to want to do is to compute the address
somewhere into the chunk pointed to by hp.

[1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100262

Upstream status: Pending
https://www.spinics.net/lists/sparclinux/msg26385.html

Signed-off-by: Romain Naour <romain.naour@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>