i2c: at91: Fix the functionality flags of the slave-only interface

i2c: at91: Fix the functionality flags of the slave-only interface

When an I2C adapter acts only as a slave, it should not claim to
support I2C master capabilities.

Fixes: 9d3ca54b550c ("i2c: at91: added slave mode support")
Signed-off-by: Jean Delvare <jdelvare@suse.de>
Cc: Juergen Fitschen <me@jue.yt>
Cc: Ludovic Desroches <ludovic.desroches@microchip.com>
Cc: Codrin Ciubotariu <codrin.ciubotariu@microchip.com>
Cc: Andi Shyti <andi.shyti@kernel.org>
Cc: Nicolas Ferre <nicolas.ferre@microchip.com>
Cc: Alexandre Belloni <alexandre.belloni@bootlin.com>
Cc: Claudiu Beznea <claudiu.beznea@tuxon.dev>
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>