mm/gup.c: fix __get_user_pages_fast() comment

mmu_gather_tlb() no longer exists.  Replace with mmu_table_batch().

Link: http://lkml.kernel.org/r/20180928053441.rpzwafzlsnp74mkl@wfg-t540p.sh.intel.comSigned-off-by: NFengguang Wu <fengguang.wu@intel.com>
Reviewed-by: NAndrew Morton <akpm@linux-foundation.org>
Cc: Jiri Kosina <trivial@kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

mm/gup.c

@@ -1817,8 +1817,8 @@ int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
 	 * interrupts disabled by get_futex_key.
 	 *
 	 * With interrupts disabled, we block page table pages from being
-	 * freed from under us. See mmu_gather_tlb in asm-generic/tlb.h
-	 * for more details.
+	 * freed from under us. See struct mmu_table_batch comments in
+	 * include/asm-generic/tlb.h for more details.
 	 *
 	 * We do not adopt an rcu_read_lock(.) here as we also want to
 	 * block IPIs that come from THPs splitting.