lima/gpir: fix warning in gpir disassembler

lima/gpir: fix warning in gpir disassembler

Fixes following warning:

../src/gallium/drivers/lima/ir/gp/disasm.c: In function ‘print_src’:
../src/gallium/drivers/lima/ir/gp/disasm.c:241:20: warning: array subscript 28 is above array bounds of ‘char[5]’ [-Warray-bounds]
  241 |              "xyzw"[src - gpir_codegen_src_attrib_x]);

Reviewed-by: Connor Abbott <cwabbott0@gmail.com>
Reviewed-by: Erico Nunes <nunes.erico@gmail.com>
Reviewed-by: Andreas Baierl <ichgeh@imkreisrum.de>
Signed-off-by: Vasily Khoruzhick <anarsoul@gmail.com>