drm/amdgpu: Fix cond_exec handling in amdgpu_ib_schedule()

drm/amdgpu: Fix cond_exec handling in amdgpu_ib_schedule()

The EXEC_COUNT field must be > 0.  In the gfx shadow
handling we always emit a cond_exec packet after the gfx_shadow
packet, but the EXEC_COUNT never gets patched.  This leads
to a hang when we try and reset queues on gfx11 APUs.

Fixes: c68cbbfd54c6 ("drm/amdgpu: cleanup conditional execution")
Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/4789
Reviewed-by: Jesse Zhang <Jesse.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>