Staging: intel_sst: return -EFAULT if copy_to_user() fails

copy_to_user() returns the number of bytes remaining to be copied but we
want to return an error code.  And that error code is -EFAULT not -EIO.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Acked-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>