vme: tsi148: Only store VME bus errors if they will be checked

The TSI148 driver provides an optional mechanism for ensuring that errors
resulting from posted transfers are caught whilst still relevant. To do this
errors are stored in a link list. If bus errors are not checked, this list
would grow until available memory had been exhausted.

Only store the errors in a link list if error detection is switched on.

Reported-by: De Roo, Steven <steven.deroo@arcelormittal.com>
Signed-off-by: Martyn Welch <martyn.welch@ge.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>