After opening the device, the first thing we should do is selecting the
input. This is because the image formats (VIDIOC_ENUM_FMT ioctl) and the
standards (VIDIOC_ENUMSTD ioctl) supported may depend on the selected
input ([1] and [2]).

[1] http://linuxtv.org/downloads/v4l-dvb-apis/vidioc-enum-fmt.html
[2] http://linuxtv.org/downloads/v4l-dvb-apis/vidioc-enumstd.htmlSigned-off-by: Stefano Sabatini <stefasab@gmail.com>