regulator: tps6586x-regulator - fix bit_mask parameter for tps6586x_set_bits()

The third parameter of tps6586x_set_bits() is the bit_mask,
thus we should use (1 << ri->go_bit) instead of ri->go_bit.

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Liam Girdwood <lrg@slimlogic.co.uk>