Staging: ipack/bridges/tpci200: check if the remove function is available

To avoid a dereference of a NULL pointer, the availability of the function is
checked before its use.

Signed-off-by: Samuel Iglesias Gonsalvez <siglesias@igalia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>