PCI: Rename extend_bridge_window() parameter

In extend_bridge_window(), change "available" parameter name to "new_size".
This makes more sense as this parameter represents the new size for the
window.  No functional change intended.

Link: https://lore.kernel.org/r/PSXP216MB043853617ECA4118C472A417803C0@PSXP216MB0438.KORP216.PROD.OUTLOOK.COM


Signed-off-by: Nicholas Johnson <nicholas.johnson-opensource@outlook.com.au>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>