sfc: Remove unnecessary use of atomic_t

We can set, get and compare-and-exchange without using atomic_t.
Change efx_mcdi_iface::state to the enum type we really wanted it to
be.

Suggested-by: David Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>

drivers/net/ethernet/sfc/mcdi.h

@@ -46,7 +46,7 @@ enum efx_mcdi_mode {
  * @resp_data_len: Response data (SDU or error) length
  */
 struct efx_mcdi_iface {
-	atomic_t state;
+	enum efx_mcdi_state state;
 	enum efx_mcdi_mode mode;
 	wait_queue_head_t wq;
 	spinlock_t iface_lock;