cmd: date: Do not overwrite arguments

Arguments are const and belong to the caller. Calling date in a hush
loop will yield different results from the second invocation.

Signed-off-by: Roman Kapl <rka@sysgo.com>
diff --git a/cmd/date.c b/cmd/date.c
index 1115b6c..7fa950a 100644
--- a/cmd/date.c
+++ b/cmd/date.c
@@ -159,18 +159,18 @@
 	int len, val;
 	char *ptr;
 
-	ptr = strchr (datestr,'.');
-	len = strlen (datestr);
+	ptr = strchr(datestr, '.');
+	len = strlen(datestr);
 
 	/* Set seconds */
 	if (ptr) {
 		int sec;
 
-		*ptr++ = '\0';
+		ptr++;
 		if ((len - (ptr - datestr)) != 2)
 			return (-1);
 
-		len = strlen (datestr);
+		len -= 3;
 
 		if (cnvrt2 (ptr, &sec))
 			return (-1);