mfd: Avoid two assignments if failures happen in tps65910_i2c_probe

In drivers/mfd/tps65910.c:tps65910_i2c_probe() there's potential for a
tiny optimization.

We assign to init_data->irq and init_data->irq_base long before we
need them, and there are two potential exits from the function before
they are needed.

Moving the assignments below these two potential exits means we
completely avoid doing them in these two (failure) cases.

Signed-off-by: Jesper Juhl <jj@chaosbits.net>
Acked-by: Graeme Gregory <gg@slimlogic.co.uk>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>