mt76: Print error message when reading EEPROM from mtd failed

When the EEPROM data is stored on a MTD partition print an error message
when reading this MTD partition failed. This is currently happening
often in OpenWrt because the initial data was written with using a flash
driver which ignores the error detection data and now OpenWrt uses a
driver which checks it.

With this patch a better error message is shown:
[    8.986988] mt7915e 0000:01:00.0: WA Firmware Version: DEV_000000, Build Time: 20201105222323
[    9.100508] mt7915e 0000:01:00.0: reading EEPROM from mtd factory failed: -117
[    9.144289] mt7915e: probe of 0000:01:00.0 failed with error -22

mt7915 does not work without an EEPROM, MT7922 still works.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Signed-off-by: Felix Fietkau <nbd@nbd.name>