mfd: dt-bindings: pm8xxx: Add new compatible string

The rtc driver now supports PM8941 PMIC device, reflect this
in the binding document.
Signed-off-by: Stanimir Varbanov <svarbanov@mm-sol.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

Documentation/devicetree/bindings/mfd/qcom,pm8xxx.txt

@@ -61,6 +61,7 @@ The below bindings specify the set of valid subnodes.
 	Definition: must be one of:
 		    "qcom,pm8058-rtc"
 		    "qcom,pm8921-rtc"
+		    "qcom,pm8941-rtc"
 
 - reg:
 	Usage: required