hidraw: Return string lengths for certain ioctls

Make HIDIOCGRAWPHYS, HIDIOCGRAWNAME, and HIDIOCGRAWUNIQ return
the length of the copied out string (including the trailing NUL
character), so they behave like their Linux hidraw counterparts.

(cherry picked from commit ed87ff4e95d92033d161e93ec1a35ce001638bae)