USB: omap_udc: Remove unneeded variable

With the current implementation omap_udc_stop is always
returning -ENODEV.

Added changes to return 0 and remove variable status.

Issue identified with coccicheck
drivers/usb/gadget/udc/omap_udc.c:2106:6-12:
Unneeded variable: "status". Return "- ENODEV" on line 2128

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