fastboot: properly handle unknown partition type

In getvar_partition_type() we attempt to find a filesystem driver for
the partition (of the list of driver enabled in U-Boot), on failure we
return the error to fastboot and completely bail out of the operation.

However, this should not be a failure, instead we should just default to
"raw". This allows commands like "fastboot format:ext4 userdata" to work
if userdata didn't already have an ext4 partition table (or if FS_EXT4
is disabled in U-Boot), as failing to determine the current partition
type is not an error in this case.

Change-Id: If60851d626f2eff598557abf6e626f36264d0eb4
Signed-off-by: Caleb Connolly <caleb.connolly@linaro.org>
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>
diff --git a/drivers/fastboot/fb_getvar.c b/drivers/fastboot/fb_getvar.c
index f65519c..d5ac164 100644
--- a/drivers/fastboot/fb_getvar.c
+++ b/drivers/fastboot/fb_getvar.c
@@ -230,7 +230,8 @@
 	if (r >= 0) {
 		r = fs_set_blk_dev_with_part(dev_desc, r);
 		if (r < 0)
-			fastboot_fail("failed to set partition", response);
+			/* If we don't know then just default to raw */
+			fastboot_okay("raw", response);
 		else
 			fastboot_okay(fs_get_type_name(), response);
 	}