input: clps711x-keypad: Changing the compatibility string to match with the smallest supported chip

This patch changes the compatibility string to match with the smallest
supported chip (EP7209). Since the DT-support for this CPU is not yet
announced, this change is safe.

Signed-off-by: Alexander Shiyan <shc_work@mail.ru>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>