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/ams-delta-fiq.c b/arch/arm/mach-omap1/ams-delta-fiq.c
index fcce7ff..31197bd2 100644
--- a/arch/arm/mach-omap1/ams-delta-fiq.c
+++ b/arch/arm/mach-omap1/ams-delta-fiq.c
@@ -102,7 +102,7 @@
 	}
 
 	retval = request_irq(INT_DEFERRED_FIQ, deferred_fiq,
-			IRQ_TYPE_EDGE_RISING, "deferred_fiq", 0);
+			IRQ_TYPE_EDGE_RISING, "deferred_fiq", NULL);
 	if (retval < 0) {
 		pr_err("Failed to get deferred_fiq IRQ, ret=%d\n", retval);
 		release_fiq(&fh);