rtc: at91rm9200: Fix syntax errors in comments

Delete the redundant word 'is'.

Signed-off-by: Xiang wangx <wangxiang@cdjrlc.com>
Link: https://lore.kernel.org/r/20220605083515.9514-1-wangxiang@cdjrlc.com


Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>