drm/amdgpu: Fix unsigned comparison with zero in gmc_v9_0_process_interrupt()

Smatch warns:
	drivers/gpu/drm/amd/amdgpu/gmc_v9_0.c:579:
	unsigned 'xcc_id' is never less than zero.

gfx_v9_4_3_ih_to_xcc_inst() returns negative numbers as well.
Fix this by changing type of xcc_id to int.

Fixes: 98b2e9ca ("drm/amdgpu: correct the vmhub index when page fault occurs")
Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@oracle.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>