drm/amd/pp: Refine function iceland_start_smu

if upload firmware failed, no matter how many times
the function runs again, the same error will be encountered.
so remove the duplicated code.

Reviewed-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Rex Zhu <Rex.Zhu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>