ARM: at91: Remove unused extern declarations

commit 157576d5 ("misc: remove atmel_tclib")
left behind this.

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Link: https://lore.kernel.org/r/20230725141105.26904-1-yuehaibing@huawei.com


Signed-off-by: Claudiu Beznea <claudiu.beznea@tuxon.dev>