uhid: Check for errors from copyin() in ioctl handlers

This is in preparation for annotating copyin() and related functions
with __result_use_check.

Reviewed by: wulf
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D43103

(cherry picked from commit b2caed2f8d699d6dc59ecf8810d945cdea148c44)