PCI: brcmstb: Do not use __GENMASK

PCI: brcmstb: Do not use __GENMASK

Define the legacy MSI interrupt bitmask as well as the non-legacy interrupt
bitmask using GENMASK and then use them in brcm_msi_set_regs() in place of
__GENMASK().

Link: https://lore.kernel.org/r/20211122190459.3189616-1-f.fainelli@gmail.com
Reported-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>