HID: fix sparse warnings

Fix these sparse warnings:
.../hid/hid-core.c:100:15: warning: incorrect type in assignment (different signedness)
.../hid/hid-core.c:100:15:    expected signed int [usertype] *value
.../hid/hid-core.c:100:15:    got unsigned int *<noident>
        by unsigned -> s32

.../hid/hid-input-quirks.c:336:10: warning: Using plain integer as NULL pointer
        by 0 -> NULL

.../hid/usbhid/hid-core.c:786:46: warning: incorrect type in argument 3 (different signedness)
.../hid/usbhid/hid-core.c:786:46:    expected int *max
.../hid/usbhid/hid-core.c:786:46:    got unsigned int *<noident>
.../hid/usbhid/hid-core.c:787:47: warning: incorrect type in argument 3 (different signedness)
.../hid/usbhid/hid-core.c:787:47:    expected int *max
.../hid/usbhid/hid-core.c:787:47:    got unsigned int *<noident>
.../hid/usbhid/hid-core.c:788:48: warning: incorrect type in argument 3 (different signedness)
.../hid/usbhid/hid-core.c:788:48:    expected int *max
.../hid/usbhid/hid-core.c:788:48:    got unsigned int *<noident>
        by int -> unsigned int

Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>