V4L/DVB (6019): cx88: Make card database more memory efficient

The vmux setting is only two bits, but was taking up a whole 32 
in the input description struct.  By changing it to a two-bit 
bitfield, it can fit in what was padding space before and drop 
the input size by 4 bytes, from 28 to 24. This drops the board 
description struct, which has 9 inputs, from 280 to 244 bytes.  
Total driver size decreases by 2108 bytes.

Signed-off-by: Trent Piepho <xyzzy@speakeasy.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>