sfc: handle VI shortage on ef100 by readjusting the channels

When fewer VIs are allocated than what is allowed we can readjust
the channels by calling efx_mcdi_alloc_vis() again.

Signed-off-by: Pieter Jansen van Vuuren <pieter.jansen-van-vuuren@amd.com>
Reviewed-by: Martin Habets <habetsm.xilinx@gmail.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Reviewed-by: Edward Cree <ecree.xilinx@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>