ARM: omap: fix prm44xx.c OMAP44XX_IRQ_PRCM build error

When CONFIG_OF is disabled, the compile fails with:

arch/arm/mach-omap2/prm44xx.c:41: error: 'OMAP44XX_IRQ_PRCM' undeclared here (not in a function)

Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>