regulator: s2mps11: Use local variable for number of regulators

Remove the s2mps11_info.rdev_num because it is not used outside of
probe.

Suggested-by: Andi Shyti <andi.shyti@samsung.com>
Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Reviewed-by: Andi Shyti <andi.shyti@samsung.com>
Signed-off-by: Mark Brown <broonie@kernel.org>