drm/amd/pm: Remove unneeded result variable

Return the value atomctrl_initialize_mc_reg_table_v2_2() directly instead
of storing it in another redundant variable.

Reported-by: Zeal Robot <zealci@zte.com.cn>
Signed-off-by: ye xingchen <ye.xingchen@zte.com.cn>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>