regulator: s2mps11: Consistently use local variable

The value under 's2mps11->ext_control_gpiod[i]' is assigned to local
variable and used in probe in one place before.  Use it consistently
later so code will be easier to read.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20190909155723.24734-1-krzk@kernel.org
Signed-off-by: Mark Brown <broonie@kernel.org>