USB: gadget: Fix crash in ci13xxx_udc.c

In isr_setup_status_phase(), driver is not checking whether
the pointer is NULL before checking udc->status. Otherwise
it leads to crash. Fix it by checking for NULL.

CRs-Fixed: 367725
Change-Id: I1a74e176671dac734899cc91b3ef6db8300e08e1
Signed-off-by: Vijayavardhan Vennapusa <vvreddy@codeaurora.org>