media: v4l2-tpg: prevent the risk of a division by zero

As reported by Coverity, the logic at tpg_precalculate_line()
blindly rescales the buffer even when scaled_witdh is equal to
zero. If this ever happens, this will cause a division by zero.

Instead, add a WARN_ON_ONCE() to trigger such cases and return
without doing any precalculation.

Fixes: 63881df94d ("[media] vivid: add the Test Pattern Generator")
Cc: stable@vger.kernel.org
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

drivers/media/common/v4l2-tpg/v4l2-tpg-core.c

@@ -1795,6 +1795,9 @@ static void tpg_precalculate_line(struct tpg_data *tpg)
 	unsigned p;
 	unsigned x;
 
+	if (WARN_ON_ONCE(!tpg->src_width || !tpg->scaled_width))
+		return;
+
 	switch (tpg->pattern) {
 	case TPG_PAT_GREEN:
 		contrast = TPG_COLOR_100_RED;