PCI: j721e: correct PCIe lane selection mask

PCIe lane mask should be based on the maximum number of lanes and not the
currently selected lane count, since we have no idea what the bootloader may
have initialized to this register.

Reported-by: Vignesh Raghavendra <vigneshr@ti.com>
Fixes: 3c97d831

 ("PCI: j721e: correct lane count mask based on lane numbers")
Signed-off-by: Matt Ranostay <mranostay@ti.com>
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>