USB: gadget: compilation issue: missing TASK_INTERRUPTIBLE

Here is the patch for the following issue:

drivers/usb/gadget/u_serial.c: In function ‘gs_start_tx’:
drivers/usb/gadget/u_serial.c:369: error: ‘TASK_INTERRUPTIBLE’ undeclared (first use in this function)
drivers/usb/gadget/u_serial.c:369: error: (Each undeclared identifier is reported only once
drivers/usb/gadget/u_serial.c:369: error: for each function it appears in.)
drivers/usb/gadget/u_serial.c: In function ‘gs_rx_push’:
drivers/usb/gadget/u_serial.c:546: error: ‘TASK_INTERRUPTIBLE’ undeclared (first use in this function)
drivers/usb/gadget/u_serial.c: In function ‘gs_close’:
drivers/usb/gadget/u_serial.c:857: error: ‘TASK_INTERRUPTIBLE’ undeclared (first use in this function)
drivers/usb/gadget/u_serial.c:857: error: implicit declaration of function ‘signal_pending’
drivers/usb/gadget/u_serial.c:857: error: implicit declaration of function ‘schedule_timeout’
drivers/usb/gadget/u_serial.c: In function ‘gserial_cleanup’:
drivers/usb/gadget/u_serial.c:1190: error: ‘TASK_UNINTERRUPTIBLE’ undeclared (first use in this function)
drivers/usb/gadget/u_serial.c:1190: error: implicit declaration of function ‘schedule’
drivers/usb/gadget/u_serial.c: In function ‘gserial_disconnect’:
drivers/usb/gadget/u_serial.c:1311: error: ‘TASK_INTERRUPTIBLE’ undeclared (first use in this function)

Signed-off-by: Stephane Duverger <stephane.duverger@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>