mtd: Unconditionally update ->fail_addr and ->addr in part_erase()

->fail_addr and ->addr can be updated no matter the result of
parent->_erase(), we just need to remove the code doing the same thing
in mtd_erase_callback() to avoid adjusting those fields twice.

Note that this can be done because all MTD users have been converted to
not pass an erase_info->callback() and are thus only taking the
->addr_fail and ->addr fields into account after part_erase() has
returned.

While we're at it, get rid of the erase_info->mtd field which was only
needed to let mtd_erase_callback() get the partition device back.

Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
Reviewed-by: Richard Weinberger <richard@nod.at>

include/linux/mtd/mtd.h

@@ -38,13 +38,14 @@
 
 #define MTD_FAIL_ADDR_UNKNOWN -1LL
 
+struct mtd_info;
+
 /*
  * If the erase fails, fail_addr might indicate exactly which block failed. If
  * fail_addr = MTD_FAIL_ADDR_UNKNOWN, the failure was not at the device level
  * or was not specific to any particular block.
  */
 struct erase_info {
-	struct mtd_info *mtd;
 	uint64_t addr;
 	uint64_t len;
 	uint64_t fail_addr;