ata: ahci: fix ahci_link_up() type mismatch for LTO

When building highbank_defconfig with LTO, the compiler complains about
type mismatch of function ahci_link_up().

The third parameter of this function is of type u8 in
drivers/ata/ahci.c, but of type int in board/highbank/ahci.c.

There is no reason in using u8, and the code using this function
actually passes an int variable into the function (so it is implicitly
converted to u8).

Change the type of this parameter to int in drivers/ata/ahci.c.

Signed-off-by: Marek Behún <marek.behun@nic.cz>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>