HID: hiddev: Remove redundant check on unsigned variable

No need to check whether unsigned variable is less than 0.

CC: Jiri Kosina <jkosina@suse.cz>
CC: linux-usb@vger.kernel.org
CC: linux-input@vger.kernel.org
Signed-off-by: Tushar Behera <tushar.behera@linaro.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>