usb: gadget: at91_udc: Remove unneeded variable

at91_wakeup is always returning -EINVAL.

But usb_gadget_wakeup expects 0 on success and negative number on
failure. As per current implementation this function wont fail.

This patch removes unneeded variable and returns 0.

Issue identified by coccicheck

drivers/usb/gadget/udc/at91_udc.c:802:6-12:
Unneeded variable: "status". Return "- EINVAL" on line 821

Signed-off-by: Hariprasad Kelam <hariprasad.kelam@gmail.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>