locks: use list_first_entry_or_null()

Simplify the code with list_first_entry_or_null().
Signed-off-by: Geliang Tang <geliangtang@163.com>
Signed-off-by: Jeff Layton <jeff.layton@primarydata.com>

fs/locks.c

@@ -1505,12 +1505,10 @@ void lease_get_mtime(struct inode *inode, struct timespec *time)
 	ctx = smp_load_acquire(&inode->i_flctx);
 	if (ctx && !list_empty_careful(&ctx->flc_lease)) {
 		spin_lock(&ctx->flc_lock);
-		if (!list_empty(&ctx->flc_lease)) {
-			fl = list_first_entry(&ctx->flc_lease,
+		fl = list_first_entry_or_null(&ctx->flc_lease,
 					      struct file_lock, fl_list);
-			if (fl->fl_type == F_WRLCK)
+		if (fl && (fl->fl_type == F_WRLCK))
 			has_lease = true;
-		}
 		spin_unlock(&ctx->flc_lock);
 	}