[media] em28xx-i2c: fix the error code for unknown errors

Commit e63b009d "em28xx-i2c: Fix error code for I2C error transfers"
changed the code to return -ETIMEDOUT on all unknown errors.
But the proper error code for unknown errors is -EIO.
So only report -ETIMEDOUT in case of the errors 0x02 and 0x04, which
are according to Mauro Carvalho Chehab's tests related to i2c clock
stretching and return -EIO for the rest.

Signed-off-by: Frank Schäfer <fschaefer.oss@googlemail.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>