mm/swapfile.c: fix swapon frontswap_map memory leak on error

Free frontswap_map if an error is encountered before enable_swap_info().

Signed-off-by: David Rientjes <rientjes@google.com>
Reviewed-by: "Huang, Ying" <ying.huang@intel.com>
Cc: Darrick J. Wong <darrick.wong@oracle.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: <stable@vger.kernel.org>	[4.12+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 12251d3..bf91dc9 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -3291,6 +3291,7 @@
 	spin_unlock(&swap_lock);
 	vfree(swap_map);
 	kvfree(cluster_info);
+	kvfree(frontswap_map);
 	if (swap_file) {
 		if (inode && S_ISREG(inode->i_mode)) {
 			inode_unlock(inode);