drm/amdgpu: Fix one kernel-doc comment

Use colon to separate parameter name from their specific meaning.
silence the warning:

drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c:793: warning: Function parameter or member 'adev' not described in 'amdgpu_vm_pte_update_noretry_flags'

Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Yang Li <yang.lee@linux.alibaba.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>