powerpc: tiny memcpy_(to|from)io optimisation

This trivial patch changes memcpy_(to|from)io as to transfer as many
32-bit words as possible in 32-bit accesses (in the current solution,
the last 32-bit word was transferred as 4 byte accesses).
Signed-off-by: Albrecht Dreß <albrecht.dress@arcor.de>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

arch/powerpc/kernel/io.c

@@ -161,7 +161,7 @@ void _memcpy_fromio(void *dest, const volatile void __iomem *src,
 		dest++;
 		n--;
 	}
-	while(n > 4) {
+	while(n >= 4) {
 		*((u32 *)dest) = *((volatile u32 *)vsrc);
 		eieio();
 		vsrc += 4;
@@ -190,7 +190,7 @@ void _memcpy_toio(volatile void __iomem *dest, const void *src, unsigned long n)
 		vdest++;
 		n--;
 	}
-	while(n > 4) {
+	while(n >= 4) {
 		*((volatile u32 *)vdest) = *((volatile u32 *)src);
 		src += 4;
 		vdest += 4;