usb: gadget: mv_u3d: fix sparse warnings

fix the following sparse warnings:

drivers/usb/gadget/mv_u3d_core.c:223:20: warning: context imbalance in 'mv_u3d_done' - unexpected unlock
drivers/usb/gadget/mv_u3d_core.c:1562:25: warning: context imbalance in 'mv_u3d_handle_setup_packet' - unexpected unlock

Note that the non-trivial sparse warnings
are left out of this commit due to lack of
HW to test:

drivers/usb/gadget/mv_u3d_core.c:906:42: warning: incorrect type in argument 2 (different address spaces)
drivers/usb/gadget/mv_u3d_core.c:906:42:    expected void [noderef] <asn:2>*<noident>
drivers/usb/gadget/mv_u3d_core.c:906:42:    got unsigned int *<noident>

Signed-off-by: Felipe Balbi <balbi@ti.com>