strftime/wcsftime: use STRLEN, not strlen

Commit 737e2004a3 accidentally introduced a call to strlen in
code used with wide character strings in case of wcsftime.  Use
STRLEN instead.

Fixes: 737e2004a3 ("strftime.c(__strftime): add %q, %v, tests; tweak %Z doc")
Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

newlib/libc/time/strftime.c

@@ -1260,7 +1260,7 @@ recurse:
 	       format. Recurse to avoid need to replicate %b and %Y formation. */
 	    CHAR fmtbuf[32], *fmt = fmtbuf;
 	    STRCPY (fmt, CQ("%e-%b-%"));
-	    fmt += strlen (fmt);
+	    fmt += STRLEN (fmt);
 	    if (pad) /* '0' or '+' */
 	      *fmt++ = pad;
 	    else