MAINTAINERS: Add maintainers for eMMC CQHCI driver

The eMMC CQHCI is the host controller interface, introduced in the eMMC
spec v5.1. The code was originally developed as collaboration among several
people, however none really stepped in to maintain it.

Let's add Adrian Hunter (Intel), Ritesh Harjani and Asutosh Das as the
maintainers, whom knows both the code and the spec.

Cc: Subhash Jadavani <subhashj@codeaurora.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Acked-by: Ritesh Harjani <riteshh@codeaurora.org>
Acked-by: Asutosh Das <asutoshd@codeaurora.org>