ARM: fix warnings about atomic64_read

Fix:
net/netfilter/xt_connbytes.c: In function 'connbytes_mt':
net/netfilter/xt_connbytes.c:43: warning: passing argument 1 of 'atomic64_read' discards qualifiers from pointer target type
...

by adding the missing const.
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/include/asm/atomic.h

@@ -243,7 +243,7 @@ typedef struct {
 
 #define ATOMIC64_INIT(i) { (i) }
 
-static inline u64 atomic64_read(atomic64_t *v)
+static inline u64 atomic64_read(const atomic64_t *v)
 {
 	u64 result;