[media] mxl111sf: fix build warning

fix build warning:
	variable ‘ret’ set but not used in function ‘mxl111sf_i2c_readagain’

Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>