fs: Rename fs_read() to fs_legacy_read()

This existing function does not have any context associated with it.
Rename it so that fs_read() can be used for the new FS uclass.

Signed-off-by: Simon Glass <sjg@chromium.org>

common/spl/spl_blk_fs.c

@@ -32,8 +32,8 @@ static ulong spl_fit_read(struct spl_load_info *load, ulong file_offset,
 		return ret;
 	}
 
-	ret = fs_read(dev->filename, virt_to_phys(buf), file_offset, size,
-		      &actlen);
+	ret = fs_legacy_read(dev->filename, virt_to_phys(buf), file_offset,
+			     size, &actlen);
 	if (ret < 0) {
 		printf("spl: error reading image %s. Err - %d\n",
 		       dev->filename, ret);