staging: vt6656: Fix (most) sparse warnings regarding static functions/variables

This fixes sparse warnings for functions and variables, e.g.:
* drivers/staging/vt6656/card.c:69:11: warning: symbol 'cwRXBCNTSFOff'
was not declared. Should it be static?

Some warnings were false positives, such as:
* drivers/staging/vt6656/dpc.c:249:5: warning: symbol 'RXbBulkInProcessData'
was not declared. Should it be static?

Signed-off-by: Valentina Manea <valentina.manea.m@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>