drm/amdgpu: Fix style issues in amdgpu_debugfs.c

Fixes the following to align to linux coding style:

WARNING: Missing a blank line after declarations
WARNING: sizeof *rd should be sizeof(*rd)

Cc: Christian König <christian.koenig@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Guchun Chen <guchun.chen@amd.com>
Signed-off-by: Praful Swarnakar <Praful.Swarnakar@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>