unprotect(), erase() and protect() return EOPNOTSUPP errno code
for at24 I2C eeproms, so envfs_save() doesn't store data
to these eeproms without this patch.
Signed-off-by: Antony Pavlov <antonynpavlov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>