zdtm/atomic: atomic_inc should return the old value

00:24:30.269:    44: ERR: test.c:208: Test exited on unexpected signal

It's a correct name for this function. For example, we use this name
here criu/arch/ppc64/include/asm/atomic.h

And you can find the same set of functions here:
test/zdtm/lib/arch/aarch64/include/asm/atomic.h

I think this code is more readable (understandable) than just
return t - 1.
Signed-off-by: Andrew Vagin <avagin@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>

test/zdtm/lib/arch/ppc64/include/asm/atomic.h

@@ -47,7 +47,7 @@ ATOMIC_OP(sub, subf)
 
 #undef ATOMIC_OP
 
-static __inline__ int atomic_inc(atomic_t *v)
+static __inline__ int atomic_inc_return(atomic_t *v)
 {
 	int t;
 
@@ -65,6 +65,11 @@ static __inline__ int atomic_inc(atomic_t *v)
 	return t;
 }
 
+static __inline__ int atomic_inc(atomic_t *v)
+{
+	return atomic_inc_return(v) - 1;
+}
+
 static __inline__ void atomic_dec(atomic_t *v)
 {
 	int t;