powerpc: fix io.h build warning with CONFIG_PHYS_64BIT

Casting a pointer to a phys_addr_t when it's an unsigned long long
on a 32-bit system without first casting to a non-pointer type
generates a compiler warning. Fix this.

Signed-off-by: Becky Bruce <beckyb@kernel.crashing.org>

include/asm-ppc/io.h

@@ -300,7 +300,7 @@ static inline void unmap_physmem(void *vaddr, unsigned long flags)
 
 static inline phys_addr_t virt_to_phys(void * vaddr)
 {
-	return (phys_addr_t)(vaddr);
+	return (phys_addr_t)((unsigned long)vaddr);
 }
 
 #endif