The low level EEPROM write method, doesn't return
1, but the number of bytes written. Thus do not
compare to 1, instead, compare to greater than 0
for success.

Other cleanup: if the lower layers returned
-errno, then return that, as opposed to
overwriting the error code with one-fits-all
-EINVAL. For instance, some return -EAGAIN.

Cc: Jean Delvare <jdelvare@suse.de>
Cc: Alexander Deucher <Alexander.Deucher@amd.com>
Cc: Andrey Grodzovsky <Andrey.Grodzovsky@amd.com>
Cc: Lijo Lazar <Lijo.Lazar@amd.com>
Cc: Stanley Yang <Stanley.Yang@amd.com>
Cc: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Luben Tuikov <luben.tuikov@amd.com>
Reviewed-by: Alexander Deucher <Alexander.Deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>