PCI: brcmstb: Fix build on 32bit ARM platforms with older compilers

PCI: brcmstb: Fix build on 32bit ARM platforms with older compilers

Some older compilers have no implementation for the helper for 64-bit
unsigned division/modulo, so linking pcie-brcmstb driver causes the
"undefined reference to `__aeabi_uldivmod'" error.

*rc_bar2_size is always a power of two, because it is calculated as:
"1ULL << fls64(entry->res->end - entry->res->start)", so the modulo
operation in the subsequent check can be replaced by a simple logical
AND with a proper mask.

Link: https://lore.kernel.org/r/20200227115146.24515-1-m.szyprowski@samsung.com
Fixes: c0452137034b ("PCI: brcmstb: Add Broadcom STB PCIe host controller driver")
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Acked-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>