MAINTAINERS: Add an additional maintainer to the AMD XGBE driver

Add Shyam Sundar S K as an additional maintainer to support the AMD XGBE
network device driver.

Cc: Shyam Sundar S K <Shyam-sundar.S-k@amd.com>
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Link: https://lore.kernel.org/r/db367f24089c2bbbcd1cec8e21af49922017a110.1657751501.git.thomas.lendacky@amd.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>