TSI148: Fix argument parsing

This patch does 2 things:
 - Fix the argument number assigned to the vdw (VME data width) value.
   Previously, a nonexistent 7th arument was read as the vdw variable.

 - Reduce the size of the argument array for the tsi148 command from
   8 to 7.  The tsi148 command itself is argument index 0, and the
   maximum number arguments passed to the command is 6, making a total
   of 7 for the array.

Signed-off-by: Brent Darley <bdarley@xes-inc.com>
Signed-off-by: Peter Tyser <ptyser@xes-inc.com>