MAINTAINERS: add myself as maintainer for b53

I wrote the original OpenWrt driver that Florian used as the base for
the dsa driver, I might as well take responsibility for it.

Signed-off-by: Jonas Gorski <jonas.gorski@gmail.com>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Link: https://patch.msgid.link/20251013180347.133246-1-jonas.gorski@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: KanjiMonster

MAINTAINERS

@@ -4804,6 +4804,7 @@ F:	drivers/net/ethernet/broadcom/b44.*
 
 BROADCOM B53/SF2 ETHERNET SWITCH DRIVER
 M:	Florian Fainelli <florian.fainelli@broadcom.com>
+M:	Jonas Gorski <jonas.gorski@gmail.com>
 L:	netdev@vger.kernel.org
 L:	openwrt-devel@lists.openwrt.org (subscribers-only)
 S:	Supported