irq: Remove superfluous NULL pointer check in check_irq_resend()

This takes care of the following entry from Dan's list:

kernel/irq/resend.c +73 check_irq_resend(17) warning: variable derefenced before check 'desc->chip'

Reported-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Eugene Teo <eteo@redhat.com>
Cc: Julia Lawall <julia@diku.dk>
LKML-Reference: <200908062146.03638.bzolnier@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>