MAINTAINERS: Move Manivannan Sadhasivam as PCI Native host bridge and endpoint maintainer

I'm currently maintaining the PCI endpoint subsystem and reviewing the
native host bridge and endpoint drivers. However, this affects my endpoint
maintainership role since I cannot merge endpoint patches that depend on
the controller drivers (which is more common). Moreover, the controller
driver patches would also benefit from a helping hand in maintaining them.

So I'd like to step up to maintain the native host bridge and endpoint
drivers together with the endpoint subsystem.

Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Link: https://patch.msgid.link/20250418094905.9983-1-manivannan.sadhasivam@linaro.org