drm/amdgpu: clear err_event_athub flag after reset exit

Otherwise next err_event_athub error cannot call gpu reset. And following
resume sequence will not be affected by this flag.

v2: create function to clear amdgpu_ras_in_intr for modularity of ras driver

Signed-off-by: Le Ma <le.ma@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>