Staging: crystalhd: use vfree() instead of kfree()

Use vfree() instead of kfree() to free vmalloc()
allocated data.

Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>