staging/easycap: kill telltale logic

This reason for this feature was

'some versions of the videodev module overwrite the data which has
been written by the call to usb_set_intfdata() in easycap_usb_probe(),
replacing it with a pointer to the embedded v4l2_device structure.
to detect this, the string in the easycap.telltale[] buffer is checked.'

The upstream version of v4l2_device_register sets driver data
only when it wasn't already set, therefore this is not needed

Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>