MAINTAINERS: Update MCAN MMIO device driver maintainer

Update Pankaj Sharma as maintainer for mcan mmio device driver as I
will be moving to a different role.

Signed-off-by: Sriram Dash <sriram.dash@samsung.com>
Acked-by: Pankaj Sharma <pankj.sharma@samsung.com>
Link: https://lore.kernel.org/r/20210104123134.16930-1-sriram.dash@samsung.com
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>