Use the correct return type for getopt

Use the correct return type for getopt otherwise clang complains
about tautological-constant-out-of-range-compare.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Sterling Jensen <sterlingjensen@users.noreply.github.com>
Closes #11359

cmd/zfs/zfs_main.c

@@ -8492,7 +8492,7 @@ zfs_do_wait(int argc, char **argv)
 {
 	boolean_t enabled[ZFS_WAIT_NUM_ACTIVITIES];
 	int error, i;
-	char c;
+	int c;
 
 	/* By default, wait for all types of activity. */
 	for (i = 0; i < ZFS_WAIT_NUM_ACTIVITIES; i++)

cmd/zfs_ids_to_path/zfs_ids_to_path.c

@@ -44,7 +44,7 @@ int
 main(int argc, char **argv)
 {
 	boolean_t verbose = B_FALSE;
-	char c;
+	int c;
 	while ((c = getopt(argc, argv, "v")) != -1) {
 		switch (c) {
 		case 'v':

cmd/zpool/zpool_main.c

@@ -10147,7 +10147,7 @@ int
 zpool_do_wait(int argc, char **argv)
 {
 	boolean_t verbose = B_FALSE;
-	char c;
+	int c;
 	char *value;
 	int i;
 	unsigned long count;

cmd/zstream/zstream_redup.c

@@ -421,7 +421,7 @@ int
 zstream_do_redup(int argc, char *argv[])
 {
 	boolean_t verbose = B_FALSE;
-	char c;
+	int c;
 
 	while ((c = getopt(argc, argv, "v")) != -1) {
 		switch (c) {