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>

cpukit/libfs/src/jffs2/src/erase.c

@@ -61,7 +61,6 @@ static void jffs2_erase_block(struct jffs2_sb_info *c,
 
 	memset(instr, 0, sizeof(*instr));
 
-	instr->mtd = c->mtd;
 	instr->addr = jeb->offset;
 	instr->len = c->sector_size;