ARM: at91: at91sam9x5 RTC is not compatible with at91rm9200 one

commit 23fb05c688a8dcb0cf6a4d8d819cffeca82e5c54 upstream.

Due to a bug with RTC IMR, we cannot consider at91sam9x5 RTC compatible
with the previous one. Modify DT compatibility string, even if the driver
is not yet modified to take it into account.

Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>