MAINTAINER, git-mailrc: Update the mmc maintainer

Update to me as co-maintainer with Peng.
Additionally, update the mmc alias in git-mailrc.

Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Peng Fan <peng.fan@nxp.com>
diff --git a/MAINTAINERS b/MAINTAINERS
index 2accd1f..5ec1e366 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -882,6 +882,7 @@
 
 MMC
 M:	Peng Fan <peng.fan@nxp.com>
+M:	Jaehoon Chung <jh80.chung@samsung.com>
 S:	Maintained
 T:	git https://source.denx.de/u-boot/custodians/u-boot-mmc.git
 F:	drivers/mmc/