docs: arm64: Fix a grammar error

depending -> depending on

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: He Ying <heying24@huawei.com>
Link: https://lore.kernel.org/r/20210330085817.86185-1-heying24@huawei.com


Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>