drm/amd/display: Clean up style problems in amdgpu_dm_irq.c

Fix the following warnings reported by checkpatch:

WARNING: Block comments use a trailing */ on a separate line
WARNING: Comparisons should place the constant on the right side of the test
WARNING: space prohibited between function name and open parenthesis '('
WARNING: Prefer 'unsigned int' to bare use of 'unsigned'

Cc: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Cc: Aurabindo Pillai <aurabindo.pillai@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Reviewed-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>