pinctrl: sh-pfc: fix property name in bindings doc

It must be "drive-strength", with a hyphen.
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>

Documentation/devicetree/bindings/pinctrl/renesas,pfc-pinctrl.txt

@@ -72,7 +72,7 @@ Pin Configuration Node Properties:
 
 The pin configuration parameters use the generic pinconf bindings defined in
 pinctrl-bindings.txt in this directory. The supported parameters are
-bias-disable, bias-pull-up, bias-pull-down, drive strength and power-source. For
+bias-disable, bias-pull-up, bias-pull-down, drive-strength and power-source. For
 pins that have a configurable I/O voltage, the power-source value should be the
 nominal I/O voltage in millivolts.