MAINTAINERS: Add myself as reviewer instead of Naga

Naga no longer works for AMD/Xilinx and there is no activity from him to
continue to maintain Xilinx related drivers. Add myself instead to be kept
in loop if there is any need for testing.

Signed-off-by: Michal Simek <michal.simek@amd.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
[<miquel.raynal@bootlin.com>: Manually apply on top of the latest -rc which
                              where the MAINTAINERS file got sorted]
Link: https://lore.kernel.org/linux-mtd/06df49c300c53a27423260e99acc217b06d4e588.1684827820.git.michal.simek@amd.com