arm64: Add cast for virt_to_pfn

virt_to_pfn lacks a cast at the top level. Don't rely on __virt_to_phys
and explicitly cast to unsigned long.
Reviewed-by: NMark Rutland <mark.rutland@arm.com>
Tested-by: NMark Rutland <mark.rutland@arm.com>
Signed-off-by: NLaura Abbott <labbott@redhat.com>
Signed-off-by: NWill Deacon <will.deacon@arm.com>

arch/arm64/include/asm/memory.h

@@ -209,7 +209,7 @@ static inline void *phys_to_virt(phys_addr_t x)
 #define __pa(x)			__virt_to_phys((unsigned long)(x))
 #define __va(x)			((void *)__phys_to_virt((phys_addr_t)(x)))
 #define pfn_to_kaddr(pfn)	__va((pfn) << PAGE_SHIFT)
-#define virt_to_pfn(x)      __phys_to_pfn(__virt_to_phys(x))
+#define virt_to_pfn(x)      __phys_to_pfn(__virt_to_phys((unsigned long)(x)))
 
 /*
  *  virt_to_page(k)	convert a _valid_ virtual address to struct page *