fs: exfat: Fix exfat_fs_exists() return value

The exfat_fs_exists() should return 0 in case the path does not exist,
and 1 in case the path does exist. Fix the inverted return value. This
fixes 'test -e' command with exfat.

Fixes: b86a651b646c ("fs: exfat: Add U-Boot porting layer")
Signed-off-by: Marek Vasut <marex@denx.de>
diff --git a/fs/exfat/io.c b/fs/exfat/io.c
index 004ba5d..43c0571 100644
--- a/fs/exfat/io.c
+++ b/fs/exfat/io.c
@@ -875,11 +875,11 @@
 
 	err = exfat_lookup_realpath(&ctxt.ef, &node, filename);
 	if (err)
-		return err;
+		return 0;
 
 	exfat_put_node(&ctxt.ef, node);
 
-	return 0;
+	return 1;
 }
 
 int exfat_fs_size(const char *filename, loff_t *size)