usb/mv_udc_core: fix compile

|drivers/usb/gadget/mv_udc_core.c:2108: error: label `error' used but not defined

This seems to be broken since the initial commit. I changed this to a
simple return. The other user is the probe code which lets ->probe()
fail on error here.

|drivers/usb/gadget/mv_udc_core.c:2107: warning: passing argument 1 of `dev_err' from incompatible pointer type
|drivers/usb/gadget/mv_udc_core.c:2118: warning: initialization from incompatible pointer type
|drivers/usb/gadget/mv_udc_core.c:2119: warning: initialization from incompatible pointer type
|drivers/usb/gadget/mv_udc_core.c:2130: error: initializer element is not constant
|drivers/usb/gadget/mv_udc_core.c:2130: error: (near initialization for `udc_driver.driver.pm')

Cc: Chao Xie <chao.xie@marvell.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>