lib/memregion.c: include memregion.h

This addresses the following sparse warning:

lib/memregion.c:8:5: warning: symbol 'memregion_alloc' was not declared. Should it be static?
lib/memregion.c:14:6: warning: symbol 'memregion_free' was not declared. Should it be static?

Reported-by: Hulk Robot <[e-mail]>
Signed-off-by: Jason Yan <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Linus Torvalds <[e-mail]>

lib/memregion.c

···
 /* identifiers for device / performance-differentiated memory regions */
 #include <linux/idr.h>
 #include <linux/types.h>
+#include <linux/memregion.h>
 
 static DEFINE_IDA(memregion_ids);