powerpc/xmon: Make symbol 'spu_inst_dump' static

Fix sparse warning:

arch/powerpc/xmon/xmon.c:4216:1: warning:
 symbol 'spu_inst_dump' was not declared. Should it be static?

This symbol is not used outside of xmon.c, so make it static.
Signed-off-by: Pu Lehui <pulehui@huawei.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210409070151.163424-1-pulehui@huawei.com

arch/powerpc/xmon/xmon.c

@@ -4188,8 +4188,7 @@ static void dump_spu_fields(struct spu *spu)
 	DUMP_FIELD(spu, "0x%p", pdata);
 }
 
-int
-spu_inst_dump(unsigned long adr, long count, int praddr)
+static int spu_inst_dump(unsigned long adr, long count, int praddr)
 {
 	return generic_inst_dump(adr, count, praddr, print_insn_spu);
 }