ubi: allow to write to volume with offset

Introduce ubi_volume_offset_write() helper, which
allow to write to ubi volume with specified offset.

Signed-off-by: Alexey Romanov <avromanov@salutedevices.com>
Reviewed-by: Heiko Schocher <hs@denx.de>
Acked-by: Heiko Schocher <hs@denx.de>
Signed-off-by: Michael Trimarchi <michael@amarulasolutions.com>
diff --git a/include/ubi_uboot.h b/include/ubi_uboot.h
index a4be0fe..d36bb92 100644
--- a/include/ubi_uboot.h
+++ b/include/ubi_uboot.h
@@ -48,7 +48,7 @@
 extern int ubi_init(void);
 extern void ubi_exit(void);
 extern int ubi_part(char *part_name, const char *vid_header_offset);
-extern int ubi_volume_write(char *volume, void *buf, size_t size);
+extern int ubi_volume_write(char *volume, void *buf, loff_t offset, size_t size);
 extern int ubi_volume_read(char *volume, char *buf, loff_t offset, size_t size);
 
 extern struct ubi_device *ubi_devices[];