usb:hsotg:samsung: Rename s3c_hsotg_disconnect function

The s3c_hsotg_disconnect_irq function has been renamed to
reflect, that it can be used not only during the host
disconnect irq.

The s3c_hsotg_disconnect shall be used as a fall back for
scenario when USB cable is unplugged and plugged to the
device.

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>