drm/msm: fix compilation error when bus_scaling disabled

The function definition for 'sde_power_data_bus_parse' is not
same as declaration, which leads to compilation errors when
the bus scaling disabled.
Update mismatched function definition of 'sde_power_data_bus_parse'.

Change-Id: I09ca6dc9cc5037bfdcb48f76d6cdab2161b67b96
Signed-off-by: Lingutla Chandrasekhar <clingutla@codeaurora.org>