gianfar: fix signedness issue

irq_of_parse_and_map() has an unsigned return type.
Testing for a negative error value doesn't work here.

Signed-off-by: Nicolas Kaiser <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/net/gianfar.c

···
 			irq_of_parse_and_map(np, 1);
 		priv->gfargrp[priv->num_grps].interruptError =
 			irq_of_parse_and_map(np,2);
-		if (priv->gfargrp[priv->num_grps].interruptTransmit < 0 ||
-			priv->gfargrp[priv->num_grps].interruptReceive < 0 ||
-			priv->gfargrp[priv->num_grps].interruptError < 0) {
+		if (priv->gfargrp[priv->num_grps].interruptTransmit == NO_IRQ ||
+		    priv->gfargrp[priv->num_grps].interruptReceive  == NO_IRQ ||
+		    priv->gfargrp[priv->num_grps].interruptError    == NO_IRQ)
 			return -EINVAL;
-		}
 	}
 
 	priv->gfargrp[priv->num_grps].grp_id = priv->num_grps;