MAINTAINERS: Add entry for Hirschmann Hellcreek Switch Driver

Add myself to cover the Hirschmann Hellcreek TSN Ethernet Switch Driver.

Suggested-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Kurt Kanzenbach <kurt@linutronix.de>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Link: https://lore.kernel.org/r/20201110071829.7467-1-kurt@linutronix.de


Signed-off-by: Jakub Kicinski <kuba@kernel.org>