iris: Fix aux assertion in resource_get_handle

iris: Fix aux assertion in resource_get_handle

iris_resource_get_handle currently asserts that the resource has an aux
state that is suitable for sharing. However, the caller of this function
can pass a flag to specify that it will handle flushing/resolving the
resource as needed for sharing. Take this flag into account when
asserting the state of the aux buffer.

Fixes: e81392868e6 ("iris/resource: Drop redundant checks for aux support")
Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/128
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/1371>