media: dvb-core: add missing buffer index check

dvb_vb2_expbuf() didn't check if the given buffer index was for a valid buffer. Add this check.

Signed-off-by: Hans Verkuil hverkuil-cisco@xs4all.nl Reported-by: Chenyuan Yang chenyuan0y@gmail.com Fixes: 7dc866df ("media: dvb-core: Use vb2_get_buffer() instead of directly access to buffers array") Reviewed-by: Benjamin Gaignard benjamin.gaignard@collabora.com Cc: stable@vger.kernel.org Signed-off-by: Mauro Carvalho Chehab mchehab+huawei@kernel.org