[iwm] Fix iwm_poll_bit() error value check in iwm_attach().

The iwm(4) iwm_poll_bit() function returns 1 on success, and 0 on failure,
whereas the iwl_poll_bit() in Linux iwlwifi returns < 0 on failure.

So the (ret < 0) check ended up ignoring any error returned by
iwm_poll_bit().

Approved by:	adrian (mentor)
Differential Revision:	https://reviews.freebsd.org/D7932

sys/dev/iwm/if_iwm.c

@@ -5762,7 +5762,7 @@ iwm_attach(device_t dev)
 				   IWM_CSR_GP_CNTRL_REG_FLAG_MAC_CLOCK_READY,
 				   IWM_CSR_GP_CNTRL_REG_FLAG_MAC_CLOCK_READY,
 				   25000);
-		if (ret < 0) {
+		if (!ret) {
 			device_printf(sc->sc_dev,
 			    "Failed to wake up the nic\n");
 			goto fail;