[media] em28xx: respect the message size constraints for i2c transfers

[media] em28xx: respect the message size constraints for i2c transfers

The em2800 can transfer up to 4 bytes per i2c message.
All other em25xx/em27xx/28xx chips can transfer at least 64 bytes per message.
I2C adapters should never split messages transferred via the I2C subsystem
into multiple message transfers, because the result will almost always NOT be
the same as when the whole data is transferred to the I2C client in a single
message.
If the message size exceeds the capabilities of the I2C adapter, -EOPNOTSUPP
should be returned.

Signed-off-by: Frank Schäfer <fschaefer.oss@googlemail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>