PCI: mediatek-gen3: Remove leftover mac_reset assert for Airoha EN7581 SoC

PCI: mediatek-gen3: Remove leftover mac_reset assert for Airoha EN7581 SoC

Remove a leftover assert for mac_reset line in mtk_pcie_en7581_power_up().

This is not harmful since EN7581 does not requires mac_reset and
mac_reset is not defined in EN7581 device tree.

Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>
Link: https://lore.kernel.org/r/20250201-pcie-en7581-remove-mac_reset-v2-1-a06786cdc683@kernel.org
[kwilczynski: commit log]
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>