staging: vt6655: fix direct dereferencing of user pointer

Sparse reported that the data from tagSCmdRequest is given by
userspace, so it should be tagged as such.

Later, we were memcomparing and dereferencing it without first copying
it, fix that as well.

Signed-off-by: Guillaume Clement <gclement@baobob.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>