ARM: fix warning caused by wrongly typed arm_dma_limit

arch/arm/mm/init.c: In function 'arm_memblock_init':
arch/arm/mm/init.c:380: warning: comparison of distinct pointer types lacks a cast

by fixing the typecast in its definition when DMA_ZONE is disabled.
This was missed in 4986e5c7 (ARM: mm: fix type of the arm_dma_limit
global variable).
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/mm/mm.h

@@ -64,7 +64,7 @@ extern void __flush_dcache_page(struct address_space *mapping, struct page *page
 #ifdef CONFIG_ZONE_DMA
 extern phys_addr_t arm_dma_limit;
 #else
-#define arm_dma_limit ((u32)~0)
+#define arm_dma_limit ((phys_addr_t)~0)
 #endif
 
 extern phys_addr_t arm_lowmem_limit;