PCI: mediatek-gen3: Change driver name to mtk-pcie-gen3

PCI: mediatek-gen3: Change driver name to mtk-pcie-gen3

driver_register() will refuse to register another driver with the same name.
This change allows pcie-mediatek-gen3 to coexist with pcie-mediatek built into
the kernel.

Link: https://lore.kernel.org/r/20220505083907.86598-1-nbd@nbd.name
Fixes: d3bf75b579b9 ("PCI: mediatek-gen3: Add MediaTek Gen3 driver for MT8192")
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: Lorenzo Pieralisi <lpieralisi@kernel.org>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Jianjun Wang <jianjun.wang@mediatek.com>