mfd: dt-bindings: qcom-pm8xxx: Rename doc file to conform to naming convention

Cc: Stanimir Varbanov <svarbanov@mm-sol.com>
Cc: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

diff --git a/Documentation/devicetree/bindings/mfd/qcom,pm8xxx.txt b/Documentation/devicetree/bindings/mfd/qcom-pm8xxx.txt
similarity index 100%
rename from Documentation/devicetree/bindings/mfd/qcom,pm8xxx.txt
rename to Documentation/devicetree/bindings/mfd/qcom-pm8xxx.txt