tests: cmd: draid: remove unused and undocumented -v

Found with -Wunused-but-set-variable on Clang trunk

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Closes openzfs#13304
(cherry picked from commit 63cb341)

tests/zfs-tests/cmd/draid/draid.c

@@ -1317,7 +1317,7 @@ draid_merge_impl(nvlist_t *allcfgs, const char *srcfilename, int *mergedp)
 static int
 draid_merge(int argc, char *argv[])
 {
-	char filename[MAXPATHLEN];
+	char filename[MAXPATHLEN] = {0};
 	int c, error, total_merged = 0;
 	nvlist_t *allcfgs;