usb: gadget: uvc: fix up uvcg_v4l2_get_unmapped_area typo

Patch "usb: gadget: uvc: rename functions to avoid conflicts with host uvc"
renamed a lot of symbols but missed one references that was inside of
an #ifdef:

drivers/usb/gadget/function/uvc_v4l2.c:363:23: error: 'uvcg_v4l2_get_unmapped_area' undeclared here (not in a function)
  .get_unmapped_area = uvcg_v4l2_get_unmapped_area,
                       ^
drivers/usb/gadget/function/uvc_v4l2.c:344:22: warning: 'uvc_v4l2_get_unmapped_area' defined but not used [-Wunused-function]
 static unsigned long uvc_v4l2_get_unmapped_area(struct file *file,
                      ^

This renames the reference according the changed function name.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: 7ea95b110811 ("usb: gadget: uvc: rename functions to avoid conflicts with host uvc")
Cc: Andrzej Pietrasiewicz <andrzej.p@samsung.com>
Cc: Michael Grzeschik <m.grzeschik@pengutronix.de>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Felipe Balbi <balbi@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>