mm/mmap: replace SHM_HUGE_MASK with MAP_HUGE_MASK inside mmap_pgoff

Commit 091d0d55b2 ("shm: fix null pointer deref when userspace
specifies invalid hugepage size") had replaced MAP_HUGE_MASK with
SHM_HUGE_MASK.  Though both of them contain the same numeric value of
0x3f, MAP_HUGE_MASK flag sounds more appropriate than the other one in
the context.  Hence change it back.

Link: http://lkml.kernel.org/r/20170404045635.616-1-khandual@linux.vnet.ibm.com
Signed-off-by: Anshuman Khandual <khandual@linux.vnet.ibm.com>
Reviewed-by: Matthew Wilcox <mawilcox@microsoft.com>
Acked-by: Balbir Singh <bsingharora@gmail.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/mmap.c

@@ -1479,7 +1479,7 @@ SYSCALL_DEFINE6(mmap_pgoff, unsigned long, addr, unsigned long, len,
 		struct user_struct *user = NULL;
 		struct hstate *hs;
 
-		hs = hstate_sizelog((flags >> MAP_HUGE_SHIFT) & SHM_HUGE_MASK);
+		hs = hstate_sizelog((flags >> MAP_HUGE_SHIFT) & MAP_HUGE_MASK);
 		if (!hs)
 			return -EINVAL;