PCI: aardvark: Drop __maybe_unused from advk_pcie_disable_phy()

This function is now always used in driver remove method, drop the
__maybe_unused attribute.

Link: https://lore.kernel.org/r/20220110015018.26359-22-kabel@kernel.org


Signed-off-by: Marek Behún <kabel@kernel.org>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>