libv4lconvert: fix RGB32 conversion

[Hans Verkuil <hverkuil@xs4all.nl>]

The RGB32 formats start with an alpha byte in memory. So before calling the
v4lconvert_rgb32_to_rgb24 or v4lconvert_rgb24_to_yuv420 function skip that initial
alpha byte so the src pointer is aligned with the first color component, since
that is what those functions expect.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>

diff --git a/lib/libv4lconvert/libv4lconvert.c b/lib/libv4lconvert/libv4lconvert.c
index cea65aa..e4aa54a 100644
--- a/lib/libv4lconvert/libv4lconvert.c
+++ b/lib/libv4lconvert/libv4lconvert.c
@@ -1132,6 +1132,7 @@ static int v4lconvert_convert_pixfmt(struct v4lconvert_data *data,
 			errno = EPIPE;
 			result = -1;
 		}
+		src++;
 		switch (dest_pix_fmt) {
 		case V4L2_PIX_FMT_RGB24:
 			v4lconvert_rgb32_to_rgb24(src, dest, width, height, 0);