ash: output: Fix fmtstr return value

Upstream commit:

    Date: Sat, 19 May 2018 02:39:44 +0800
    output: Fix fmtstr return value

    The function fmtstr is meant to return the actual length of output
    produced, rather than the untruncated length.

    Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

shell/ash.c

@@ -713,7 +713,7 @@ fmtstr(char *outbuf, size_t length, const char *fmt, ...)
 	ret = vsnprintf(outbuf, length, fmt, ap);
 	va_end(ap);
 	INT_ON;
-	return ret;
+	return ret > (int)length ? length : ret;
 }
 
 static void