drm/amdgpu: Clean up errors in vega20_ih.c

Fix the following errors reported by checkpatch:

ERROR: trailing statements should be on next line
ERROR: that open brace { should be on the previous line

Signed-off-by: Ran Sun <sunran001@208suo.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>