regulator: qcom_spmi: Always return a selector when asked

I had a thinko in spmi_regulator_select_voltage_same_range() when
converting it to return selectors via the function's return value
instead of by modifying a pointer argument. I only tested
multi-range regulators so this passed through testing. Fix it by
returning the selector here.

Fixes: 1b5b1968 ("regulator: qcom_spmi: Only use selector based regulator ops")
Reported-by: Rajendra Nayak <rnayak@codeaurora.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Mark Brown <broonie@kernel.org>