PCI: Avoid accessing memory outside the ROM BAR

pci_get_rom_size() accepts the base and size of the ROM BAR as arguments.
The byte at "rom + size" is the first byte *past* the ROM, so change ">" to
">=" to avoid accessing beyond the actual length of the ROM BAR.

Signed-off-by: Rex Zhu <Rex.Zhu@amd.com>
[bhelgaas: changelog]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>