regulator: ti-abb: Fix operator precedence typo

commit 40b1936e (regulator: Introduce TI Adaptive Body Bias(ABB) on-chip
LDO driver) missed a pair of brackets which cause the wrong vset data to be
picked up from efuse, resulting in bad VBB voltage values.

Signed-off-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Mark Brown <broonie@linaro.org>
Cc: stable@vger.kernel.org