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 <[e-mail]>
Signed-off-by: Bixuan Cui <[e-mail]>
Signed-off-by: Michael Ellerman <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

arch/powerpc/platforms/pseries/pmem.c

···
 	return rc;
 }
 
-const struct of_device_id drc_pmem_match[] = {
+static const struct of_device_id drc_pmem_match[] = {
 	{ .type = "ibm,persistent-memory", },
 	{}
 };