usb:hsotg:samsung: Add release function for hsotg device

Add release function to prevent kernel warning.
Kfree is performed when all references are gone.

Signed-off-by: Sangwook Lee <sangwook.lee@linaro.org>
Signed-off-by: Lukasz Majewski <l.majewski@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>