pcmcia/bfin_cf: don't check platform_get_irq's return value against zero

platform_get_irq returns -ENXIO on failure, so !irq was probably
always true.  Better use irq <= 0.  Note that a return value of
zero is still handled as error even though this could mean irq0.

This is a followup to 305b3228 that
changed the return value of platform_get_irq from 0 to -ENXIO on error.
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Cc: David Vrabel <dvrabel@arcom.com>
Cc: Greg Kroah-Hartman <gregkh@suse.de>
Cc: Rafael J. Wysocki <rjw@sisk.pl>
Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>

drivers/pcmcia/bfin_cf_pcmcia.c

@@ -205,7 +205,7 @@ static int __devinit bfin_cf_probe(struct platform_device *pdev)
 	dev_info(&pdev->dev, "Blackfin CompactFlash/PCMCIA Socket Driver\n");
 
 	irq = platform_get_irq(pdev, 0);
-	if (!irq)
+	if (irq <= 0)
 		return -EINVAL;
 
 	cd_pfx = platform_get_irq(pdev, 1);	/*Card Detect GPIO PIN */