USB HID: clarify static quirk handling as squirks

Rename existing quirks handling code that operates over a static array
to "squirks" (short for static quirks) to differentiate it from the
dynamically-allocated quirks that will be introduced in the
next patch.  Add an accessor function specifically for static quirks,
usbhid_exists_squirk().

Signed-off-by: Paul Walmsley <paul@booyaka.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>