mm: slub: add type casting in alloc_trace_locations to avoid build warning

Add type casting in alloc_trace_locations to avoid build below warning.

mm/slub.c: In function ‘alloc_trace_locations’:
mm/slub.c:6322:27: warning: format ‘%p’ expects argument of type ‘void *’, but argument 3 has type ‘long unsigned int’ [-Wformat=]
error, forbidden warning: slub.c:6322.

Change-Id: I87e337cc73c36274aaaa8dfd384f3f80f0d2d79d
Signed-off-by: Faiyaz Mohammed <faiyazm@codeaurora.org>