staging/bcm: two information leaks in ioctl

There are a couple paths where we don't check how much data we copy back
to the user.

Cc: Dave Jones <davej@redhat.com>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>