pinctrl: qcom: spmi-gpio: Correct power_source range check

Power source selection in DIG_VIN_CTL is indexed from 0, in the range
check it shouldn't be equal to the total number of power sources.

Change-Id: Ic9666576d191e9dd0e267e96d5b4fc5a97c5b077
Signed-off-by: Fenglin Wu <fenglinw@codeaurora.org>