drm/amd/powerplay: Change assignment for a buffer variable in phm_dispatch_table() v2

The variable "temp_storage" was eventually reassigned with a pointer.
Thus omit the explicit initialisation at the beginning.

v2: agd: fix coding style

Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>