MAINTAINERS: Add Manivannan Sadhasivam as Qcom PCIe RC maintainer

Stan is moving out of mm-sol and decided not to carry on the maintainership
duties of the Qcom PCIe RC driver. Since I'm already maintaining the Qcom
PCIe EP driver, I'm volunteering myself to maintain the RC driver also.

Link: https://lore.kernel.org/r/20221028160029.44483-1-manivannan.sadhasivam@linaro.org
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: Stanimir Varbanov <svarbanov@mm-sol.com>