drm/amd/display: Use swap() instead of open coding it

Swap is a function interface that provides exchange function. To avoid
code duplication, we can use swap function.

./drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c:359:57-58: WARNING opportunity for swap().

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Link: https://bugzilla.openanolis.cn/show_bug.cgi?id=4448


Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Signed-off-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>