drm/amd/powerplay: Remove useless variable

The result variable is initialized at the beginning of the function, but
its value does not change during the function execution. Thus, remove the
variable and return the SUCCESS value, which is 0.

Issue found by coccinelle script:
* Unneeded variable: "result". Return "0"

Path to the cocci script: scripts/coccinelle/misc/returnvar.cocci

Signed-off-by: Georgiana Chelu <georgiana.chelu93@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>