mtd: fix 'part' field data corruption in mtd_info

mtd: fix 'part' field data corruption in mtd_info

[ Upstream commit 509304f4379b1c7a83f10194606aa58d937289e0 ]

Commit e7e29537a829 ("mtd: implement proper partition handling")
started using "mtd_get_master_ofs()" in mtd callbacks to determine
memory offsets by means of 'part' field from mtd_info, what previously
was smashed accessing 'master' field in the mtd_set_dev_defaults() method.
That provides wrong offset what causes hardware access errors.

Just make 'part', 'master' as separate fields, rather than using
union type to avoid 'part' data corruption when mtd_set_dev_defaults()
is called.

Fixes: e7e29537a829 ("mtd: implement proper partition handling")
Signed-off-by: Oleksandr Ocheretnyi <oocheret@cisco.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20220417184649.449289-1-oocheret@cisco.com
Signed-off-by: Sasha Levin <sashal@kernel.org>