Fix atomic_clear_long_excl wrong return

When clearing a bit, we should check whether that bit is 0.
Note atomic_clear_long_excl is not used.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Ryan Moeller <ryan@ixsystems.com>
Signed-off-by: Liu Qing <winglq@gmail.com>
Closes openzfs#10526

lib/libspl/asm-generic/atomic.c

@@ -415,7 +415,7 @@ atomic_clear_long_excl(volatile ulong_t *target, uint_t value)
 
 	VERIFY3S(pthread_mutex_lock(&atomic_lock), ==, 0);
 	bit = (1UL << value);
-	if ((*target & bit) != 0) {
+	if ((*target & bit) == 0) {
 		VERIFY3S(pthread_mutex_unlock(&atomic_lock), ==, 0);
 		return (-1);
 	}