Staging: rt2860: usb_main_dev: remove casts from void*

Remove unnesessary casts from void*.

Signed-off-by: Kulikov Vasiliy <segooon@gmail.com>
Reviewed-by: Simon Horman <horms@verge.net.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>