staging: dt3155v4l: make q_ops static

Since q_ops is only referenced in dt3155v4l.c, mark it as static.

This removes the following sparse warning:
drivers/staging/media/dt3155v4l//dt3155v4l.c:302:22: warning: symbol 'q_ops' was not declared. Should it be static?

Signed-off-by: Kristina Martšenko <kristina.martsenko@gmail.com>
Signed-off-by: Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@intel.com>