powerpc/pseries/pmem: Make symbol 'drc_pmem_match' static

The sparse tool complains as follows:

arch/powerpc/platforms/pseries/pmem.c:142:27: warning:
 symbol 'drc_pmem_match' was not declared. Should it be static?

This symbol is not used outside of pmem.c, so this
commit marks it static.
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Bixuan Cui <cuibixuan@huawei.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210409090114.59396-1-cuibixuan@huawei.com

arch/powerpc/platforms/pseries/pmem.c

@@ -139,7 +139,7 @@ int dlpar_hp_pmem(struct pseries_hp_errorlog *hp_elog)
 	return rc;
 }
 
-const struct of_device_id drc_pmem_match[] = {
+static const struct of_device_id drc_pmem_match[] = {
 	{ .type = "ibm,persistent-memory", },
 	{}
 };