usb: remove use of __devexit

CONFIG_HOTPLUG is going away as an option so __devexit is no
longer needed.

Signed-off-by: Bill Pemberton <wfp5p@virginia.edu>
Cc: Peter Korsgaard <jacmet@sunsite.dk>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Acked-by: Felipe Balbi <balbi@ti.com>
Cc: Li Yang <leoli@freescale.com>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Wan ZongShun <mcuos.com@gmail.com>
Cc: Ben Dooks <ben-linux@fluff.org>
Cc: Kukjin Kim <kgene.kim@samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>