Staging: vme: Allow override of geographical address on ca91c142

Geographical addressing only works if the VME backplane supports it. There
are a large number of old backplanes which do not support geographical
addressing. These boards will generally report a slot ID of zero - which is
an invalid ID in the slot numbering scheme.

Allow the geographical address to be over-ridden on the ca91c142 so that a
slot ID can be provided manually in these circumstances.

Signed-off-by: Martyn Welch <martyn.welch@gefanuc.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>