drm/msm: Change nested function to static function

There is currently a nested function in Russel King's tree
for the msm HDMI driver.

The last nested function was removed from the Linux kernel
when the Thinkpad driver was fixed.

I believe nested functions are not desired upstream, and it
also breaks compilation with clang so here is a patch to
change the nested function into static function. The patch
works with both clang and gcc.

Signed-off-by: Mark Charlebois <charlebm@gmail.com>
Signed-off-by: Rob Clark <robdclark@gmail.com>