Fix the err() arguments for a nfssvc(8) failure.

argv has been incremented during argument handling, so elements of the
array are no longer valid. Change the err() arguments so only the
first string pointer in argv is used.
Found during code inspection.

usr.sbin/pnfsdscopymr/pnfsdscopymr.c

@@ -295,7 +295,7 @@ main(int argc, char *argv[])
 	pnfsdarg.mdspath = *argv;
 	ret = nfssvc(NFSSVC_PNFSDS, &pnfsdarg);
 	if (ret < 0 && errno != EEXIST)
-		err(1, "Copymr failed args %s, %s", argv[1], argv[2]);
+		err(1, "Copymr failed for file %s", *argv);
 	exit(0);
 }