swscale/swscale: fix srcStride/srcSlice typo

Fixes part of Ticket3466
Found by: Andrey_Karpov / PVS-Studio
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/mjpegen: Fix declared argument size

Fixes part of Ticket3466
Found-by: Andrey_Karpov / PVS-Studio
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>