s390/time: fix get_tod_clock_ext inline assembly

The get_tod_clock_ext inline assembly does not specify its output
operands correctly. This can cause incorrect code to be generated.

Cc: stable@vger.kernel.org # 3.12
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/include/asm/timex.h

@@ -71,9 +71,11 @@ static inline void local_tick_enable(unsigned long long comp)
 
 typedef unsigned long long cycles_t;
 
-static inline void get_tod_clock_ext(char *clk)
+static inline void get_tod_clock_ext(char clk[16])
 {
-	asm volatile("stcke %0" : "=Q" (*clk) : : "cc");
+	typedef struct { char _[sizeof(clk)]; } addrtype;
+
+	asm volatile("stcke %0" : "=Q" (*(addrtype *) clk) : : "cc");
 }
 
 static inline unsigned long long get_tod_clock(void)