ARM: OMAP: fix 'using plain integer as NULL pointer' sparse warnings

sparse warns when 0 is passed to a function expecting a pointer argument.
Resolve these warnings by replacing the 0 with NULL.

arch/arm/plat-omap/include/plat/dmtimer.h:319:34: warning: Using plain integer as NULL pointer
arch/arm/plat-omap/include/plat/dmtimer.h:324:35: warning: Using plain integer as NULL pointer
arch/arm/mach-omap2/irq.c:294:22: warning: Using plain integer as NULL pointer
arch/arm/mach-omap1/board-palmz71.c:292:50: warning: Using plain integer as NULL pointer
arch/arm/mach-omap1/board-palmz71.c:295:73: warning: Using plain integer as NULL pointer
arch/arm/mach-omap1/ams-delta-fiq.c:105:63: warning: Using plain integer as NULL pointer

Signed-off-by: Paul Walmsley <paul@pwsan.com>

diff --git a/arch/arm/mach-omap1/board-palmz71.c b/arch/arm/mach-omap1/board-palmz71.c
index a2c5abc..61ed4f0 100644
--- a/arch/arm/mach-omap1/board-palmz71.c
+++ b/arch/arm/mach-omap1/board-palmz71.c
@@ -289,10 +289,10 @@
 		gpio_direction_input(PALMZ71_USBDETECT_GPIO);
 		if (request_irq(gpio_to_irq(PALMZ71_USBDETECT_GPIO),
 				palmz71_powercable, IRQF_SAMPLE_RANDOM,
-				"palmz71-cable", 0))
+				"palmz71-cable", NULL))
 			printk(KERN_ERR
 					"IRQ request for power cable failed!\n");
-		palmz71_powercable(gpio_to_irq(PALMZ71_USBDETECT_GPIO), 0);
+		palmz71_powercable(gpio_to_irq(PALMZ71_USBDETECT_GPIO), NULL);
 	}
 }