Correct level handling in zstream recompress.

sscanf returns number of items parsed on success and EOF on failure.

Reviewed-by: Adam Moss <c@yotes.com>
Reviewed-by: Paul Dagnelie <pcd@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Rob Norris <robn@despairlabs.com>
Signed-off-by: Rich Ercolani <rincebrain@gmail.com>
Closes openzfs#16198

cmd/zstream/zstream_recompress.c

@@ -77,7 +77,7 @@ zstream_do_recompress(int argc, char *argv[])
 	while ((c = getopt(argc, argv, "l:")) != -1) {
 		switch (c) {
 		case 'l':
-			if (sscanf(optarg, "%d", &level) != 0) {
+			if (sscanf(optarg, "%d", &level) != 1) {
 				fprintf(stderr,
 				    "failed to parse level '%s'\n",
 				    optarg);