drm/amd/amdgpu: Fix style issues in amdgpu_discovery.c

Fix following checkpatch errors in amdgpu_discovery.c

ERROR: space required after that ',' (ctx:VxV)
ERROR: space required before the open parenthesis '('
ERROR: code indent should use tabs where possible

Cc: Christian König <christian.koenig@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>