wimax: fix gcc warnings in sh4 when calling BUG()

SH4's BUG() seems to confuse the compiler as it is considered to
return; thus, some functions would trigger usage of uninitialized
variables or non-void functions returning void.

Work around by initializing/returning.

Signed-off-by: Inaky Perez-Gonzalez <inaky@linux.intel.com>
diff --git a/drivers/net/wimax/i2400m/op-rfkill.c b/drivers/net/wimax/i2400m/op-rfkill.c
index 487ec58..43927b5 100644
--- a/drivers/net/wimax/i2400m/op-rfkill.c
+++ b/drivers/net/wimax/i2400m/op-rfkill.c
@@ -54,8 +54,10 @@
 		/* state == WIMAX_RF_ON */
 		return i2400m->state != I2400M_SS_RF_OFF
 			&& i2400m->state != I2400M_SS_RF_SHUTDOWN;
-	else
+	else {
 		BUG();
+		return -EINVAL;	/* shut gcc warnings on certain arches */
+	}
 }