mm/swapfile.c: remove the extra check in scan_swap_map_slots()

scan_swap_map_slots() is only called by scan_swap_map() and
get_swap_pages().  Both ensure nr would not exceed SWAP_BATCH.

Just remove it.
Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Hugh Dickins <hughd@google.com>
Link: http://lkml.kernel.org/r/20200325220309.9803-2-richard.weiyang@gmail.comSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/swapfile.c

@@ -740,9 +740,6 @@ static int scan_swap_map_slots(struct swap_info_struct *si,
 	int latency_ration = LATENCY_LIMIT;
 	int n_ret = 0;
 
-	if (nr > SWAP_BATCH)
-		nr = SWAP_BATCH;
-
 	/*
 	 * We try to cluster swap pages by allocating them sequentially
 	 * in swap.  Once we've allocated SWAPFILE_CLUSTER pages this