media: v4l2-dv-timings: prevent possible overflow in v4l2_detect_gtf()

commit 3edd1fc48d2c045e8259561797c89fe78f01717e upstream.

In v4l2_detect_gtf(), it seems safer to cast the 32-bit image_width
variable to the 64-bit type u64 before multiplying to avoid
a possible overflow. The resulting object code even seems to
look better, at least on x86_64.

Found by Linux Verification Center (linuxtesting.org) with Svace.

[Sergey: rewrote the patch subject/descripition]

Fixes: c9bc9f50 ("[media] v4l2-dv-timings: fix overflow in gtf timings calculation")
Cc: stable@vger.kernel.org
Signed-off-by: Karina Yankevich <k.yankevich@omp.ru>
Signed-off-by: Sergey Shtylyov <s.shtylyov@omp.ru>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>