staging: vt6656: Use __releases/__acquires annotations

This patch fixes the following sparse warnings:

drivers/staging/vt6656/usbpipe.c:147:24: warning: context imbalance in 'PIPEnsControlOut' - unexpected unlock
drivers/staging/vt6656/usbpipe.c:209:24: warning: context imbalance in 'PIPEnsControlIn' - unexpected unlock

Signed-off-by: Iulia Manda <iulia.manda21@gmail.com>
Signed-off-by: Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@intel.com>