mfd: Allow the board to choose any GPIO base for tps65010

If the board does not care where the TPS turns up, then specifiying the
value -1 to get gpiolib to dynamically allocate the base for the chip
is valid.

Change the test to look for != 0, so that any boards specifying zero
will not end up with gpio that they didn't want.

Signed-off-by: Ben Dooks <ben@simtec.co.uk>
Signed-off-by: Simtec Liunx Team <linux@simtec.co.uk>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>