ehea: replace with page_shift() in ehea_is_hugepage()

The function page_shift() is supported after the commit 94ad9338


("mm: introduce page_shift()").

So replace with page_shift() in ehea_is_hugepage() for readability.

Signed-off-by: Yunfeng Ye <yeyunfeng@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>