LinuxKPI: Fix resource leak on pci_iounmap-ing of PCI BAR

If the resource was allocated with want_iomap_res flag set.

Sponsored by: Serenity CyberSecurity, LLC
MFC after: 1 week
Reviewed by: manu, bz
Differential Revision: https://reviews.freebsd.org/D45905

(cherry picked from commit 14fc33ea3a0571ca70e609b6f9e67db39f7c6140)