Staging: rspiusb: copy_to/from_user related fixes

The patch does copy_to/from_user related fixes

*) __copy_from/to_user is enough for user space data buffer checked by access_ok.
*) return -EFAULT if __copy_from/to_user fails.
*) Do not use memcpy to copy from user space.

Signed-off-by: Vibi Sreenivasan <vibi_sreenivasan@cms.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>