[MIPS] Fix atomic.h build errors.

For the definition of atomic64_t atomic.h was relying on <asm/types.h>
having been included previously.  Before changeset
d89d8e0637a5e4e0a12e90c4bc934d0d4c335239 this was happening as a
side effect of including <linux/spinlock.h>.
Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

include/asm-mips/atomic.h

@@ -375,7 +375,7 @@ static __inline__ int atomic_sub_if_positive(int i, atomic_t * v)
 
 #ifdef CONFIG_64BIT
 
-typedef struct { volatile __s64 counter; } atomic64_t;
+typedef struct { volatile long counter; } atomic64_t;
 
 #define ATOMIC64_INIT(i)    { (i) }