arm64: mm: use arm64_dma_phys_limit instead of calling max_zone_dma_phys()

By the time we call zones_sizes_init() arm64_dma_phys_limit already
contains the result of max_zone_dma_phys(). We use the variable instead
of calling the function directly to save some precious cpu time.
Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/mm/init.c

@@ -187,7 +187,7 @@ static void __init zone_sizes_init(unsigned long min, unsigned long max)
 	unsigned long max_zone_pfns[MAX_NR_ZONES]  = {0};
 
 #ifdef CONFIG_ZONE_DMA32
-	max_zone_pfns[ZONE_DMA32] = PFN_DOWN(max_zone_dma_phys());
+	max_zone_pfns[ZONE_DMA32] = PFN_DOWN(arm64_dma_phys_limit);
 #endif
 	max_zone_pfns[ZONE_NORMAL] = max;