V4L/DVB (6631): xc2028: eliminate i2c macro side-effects

The I2C macros have side effects and send_seq could cause a return from
a function with a mutex held.  Change them to behave like real functions.

Signed-off-by: Chris Pascoe <c.pascoe@itee.uq.edu.au>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>