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-twl4030.c b/drivers/rtc/rtc-twl4030.c
index 01d8da9..8ce5f74 100644
--- a/drivers/rtc/rtc-twl4030.c
+++ b/drivers/rtc/rtc-twl4030.c
@@ -19,6 +19,7 @@
  */
 
 #include <linux/kernel.h>
+#include <linux/errno.h>
 #include <linux/init.h>
 #include <linux/module.h>
 #include <linux/types.h>
@@ -415,8 +416,8 @@
 	int irq = platform_get_irq(pdev, 0);
 	u8 rd_reg;
 
-	if (irq < 0)
-		return irq;
+	if (irq <= 0)
+		return -EINVAL;
 
 	rtc = rtc_device_register(pdev->name,
 				  &pdev->dev, &twl4030_rtc_ops, THIS_MODULE);