drm/amd/pm/powerplay/smumgr: use bitwise or for addition

For bit mask addition, it is recommended to use or operator "|" instead
of numerical addition as the former is quicker and cleaner. Change
suggested by orplus.cocci Coccinelle semantic patch.

Reviewed-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Deepak R Varma <drv@mailo.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>