Specify the index for ENUMINPUT

If the index is not initialized, then whatever is currently occupying
that stack address will be used for index value. But only index = 0 is
valid.

Also, initialize to zero some of the reserved fields, as required by the
docs.

Test: dumpsys input (and ensure that video device is associated with the
touch input device)
Test: review v4l docs for all ioctl's used
Fixes: 128854899

Change-Id: I7e1c4cf4598428251ae5ce2ea379cdaceb0134c3