dt-bindings: qcom: Fix warning with duplicate dt define

arch/arm/boot/dts/include/dt-bindings/clock/qcom,mmcc-msm8974.h:60:0:
warning: "RBCPR_CLK_SRC" redefined

Rename this to MMSS_RBCPR_CLK_SRC to avoid conflicts with the
RBCPR clock in the gcc header.

Reported-by: Bjorn Andersson <bjorn.andersson@sonymobile.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Mike Turquette <mturquette@linaro.org>