rtc: bunch of drivers: fix 'no irq' case handing

This patch fixes a bunch of irq checking misuses.  Most drivers were
getting irq via platform_get_irq(), which returns -ENXIO or r->start.

rtc-cmos.c is special.  It is using PNP and platform bindings.  Hopefully
nobody is using PNP IRQ 0 for RTC.  So the changes should be safe.

rtc-sh.c is using platform_get_irq, but was storing a result into an
unsigned type, then was checking for < 0.  This is fixed now.

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Acked-by: David Brownell <dbrownell@users.sourceforge.net>
Acked-by: Paul Mundt <lethal@linux-sh.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/drivers/rtc/rtc-m48t59.c b/drivers/rtc/rtc-m48t59.c
index 43afb7a..33921a6 100644
--- a/drivers/rtc/rtc-m48t59.c
+++ b/drivers/rtc/rtc-m48t59.c
@@ -450,7 +450,7 @@
 	 * the mode without IRQ.
 	 */
 	m48t59->irq = platform_get_irq(pdev, 0);
-	if (m48t59->irq < 0)
+	if (m48t59->irq <= 0)
 		m48t59->irq = NO_IRQ;
 
 	if (m48t59->irq != NO_IRQ) {