HID: input: Make hidinput_find_field() static

This function is not called outside of hid-input.c so we can make it
static.

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Tero Kristo <tero.kristo@linux.intel.com>
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Link: https://lore.kernel.org/r/20211210111138.1248187-5-tero.kristo@linux.intel.com