MAINTAINERS: Add Aksh Garg as PCIe CADENCE reviewer

I wish to contribute to the review process for Cadence PCIe IP drivers,
hence add myself as a reviewer.

Signed-off-by: Aksh Garg <a-garg7@ti.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Link: https://patch.msgid.link/20260508060951.840233-1-a-garg7@ti.com