usb: gadget: s3c-hsotg: fix spinlock locking

This patch adds missing spinlock locking in s3c_hsotg_complete_setup function,
and unlocking for gadget setup call.

Signed-off-by: Robert Baldyga <r.baldyga@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>