Input: tca6416-keypad - remove an unused field in struct tca6416_keypad_chip

In "struct tca6416_keypad_chip", the 'irqnum' field is unused.
Remove it.

Found with cppcheck, unusedStructMember.
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/926c0f40040671565dcc54d5146a8f9511fb6d46.1714541432.git.christophe.jaillet@wanadoo.frSigned-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/keyboard/tca6416-keypad.c

@@ -45,7 +45,6 @@ struct tca6416_keypad_chip {
 	struct i2c_client *client;
 	struct input_dev *input;
 	int io_size;
-	int irqnum;
 	u16 pinmask;
 	bool use_polling;
 	struct tca6416_button buttons[];