Fix minor compiler warnings

These compiler warnings were introduced when code which was
previously #ifdef'ed out by HAVE_ZPL was re-added for use
by the posix layer.  All of the following changes should be
obviously correct and will cause no semantic changes.

cmd/zinject/zinject.c

@@ -566,7 +566,7 @@ main(int argc, char **argv)
 	zinject_record_t record = { 0 };
 	char pool[MAXNAMELEN];
 	char dataset[MAXNAMELEN];
-	zfs_handle_t *zhp;
+	zfs_handle_t *zhp = NULL;
 	int nowrites = 0;
 	int dur_txg = 0;
 	int dur_secs = 0;