fs: ext4: check the minimal partition size to mount

No need to mount a too small partition to handle a EXT4 file system.

This patch add a test on partition size before to read the
SUPERBLOCK_SIZE buffer and avoid error latter in fs_devread() function.

Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>

fs/ext4/ext4_common.c

@@ -2373,6 +2373,10 @@ int ext4fs_mount(unsigned part_length)
 	struct ext2_data *data;
 	int status;
 	struct ext_filesystem *fs = get_fs();
+
+	if (part_length < SUPERBLOCK_SIZE)
+		return 0;
+
 	data = zalloc(SUPERBLOCK_SIZE);
 	if (!data)
 		return 0;