ARM: integrator/versatile: fix NOMMU warnings

On NOMMU kernels, the io_desc variables are unused
because we don't use the MMU to remap the MMIO
areas.

Marking these variables as __maybe_unused easily
avoids the otherwise harmless warnings like

warning: 'versatile_io_desc' defined but not used

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Russell King <linux@arm.linux.org.uk>
diff --git a/arch/arm/mach-integrator/integrator_cp.c b/arch/arm/mach-integrator/integrator_cp.c
index 7322838..01a888d 100644
--- a/arch/arm/mach-integrator/integrator_cp.c
+++ b/arch/arm/mach-integrator/integrator_cp.c
@@ -78,7 +78,7 @@
  * fcb00000	cb000000	CP system control
  */
 
-static struct map_desc intcp_io_desc[] __initdata = {
+static struct map_desc intcp_io_desc[] __initdata __maybe_unused = {
 	{
 		.virtual	= IO_ADDRESS(INTEGRATOR_HDR_BASE),
 		.pfn		= __phys_to_pfn(INTEGRATOR_HDR_BASE),