Use core_addr_to_string_nz in csky_analyze_prologue

Use core_addr_to_string_nz in csky_analyze_prologue

One of the buildbot builders had a failure on a recent try run:

../../binutils-gdb/gdb/csky-tdep.c: In function CORE_ADDR csky_analyze_prologue(gdbarch*, CORE_ADDR, CORE_ADDR, CORE_ADDR, frame_info*, csky_unwind_cache*, lr_type_t):
../../binutils-gdb/gdb/csky-tdep.c:1107:23: error: format %lx expects argument of type long unsigned int, but argument 3 has type CORE_ADDR {aka long long unsigned int} [-Werror=format=]
        "0x%lx\n", addr);
                       ^
../../binutils-gdb/gdb/csky-tdep.c:1419:12: error: format %lx expects argument of type long unsigned int, but argument 3 has type CORE_ADDR {aka long long unsigned int} [-Werror=format=]
        addr);
            ^

The fix is to use core_addr_to_string_nz rather than %lx in
csky-tdep.c.

Tested by rebuilding.  I'm checking this in.

gdb/ChangeLog
2018-08-29  Tom Tromey  <tom@tromey.com>

	* csky-tdep.c (csky_analyze_prologue): Use
	core_addr_to_string_nz.