Input: ili210x - fix permissions on "calibrate" attribute

commit b27c0d0c3bf3073e8ae19875eb1d3755c5e8c072 upstream.

"calibrate" attribute does not provide "show" methods and thus we should
not mark it as readable.

Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Willy Tarreau <w@1wt.eu>