ext4: implement exists() for ext4fs

This hooks into the generic "file exists" support added in an earlier
patch, and provides an implementation for the ext4 filesystem.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Simon Glass <sjg@chromium.org>
diff --git a/fs/ext4/ext4fs.c b/fs/ext4/ext4fs.c
index 735b256..417ce7b 100644
--- a/fs/ext4/ext4fs.c
+++ b/fs/ext4/ext4fs.c
@@ -174,6 +174,14 @@
 	return 0;
 }
 
+int ext4fs_exists(const char *filename)
+{
+	int file_len;
+
+	file_len = ext4fs_open(filename);
+	return file_len >= 0;
+}
+
 int ext4fs_read(char *buf, unsigned len)
 {
 	if (ext4fs_root == NULL || ext4fs_file == NULL)