HID: simplify an index check in hid_lookup_collection

Save the struct hid_collection * in a temporary to shorten
the generated code a bit and perhaps improve readability.

$ size drivers/hid/hid-core.o*
   text	   data	    bss	    dec	    hex	filename
  16460	     78	      8	  16546	   40a2	drivers/hid/hid-core.o.new
  16469	     78	      8	  16555	   40ab	drivers/hid/hid-core.o.old

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>