linuxkpi: Fix pcie_set_readrq()

We were passing a LinuxKPI struct device * to a pci(4) function that
expects a device_t.

Reviewed by: manu, hselasky, bz
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D29675

(cherry picked from commit 3f322b22e02d6aae147e9948ab50ca1bee9a9dd4)