MAINTAINERS: update cxgb4 and cxgb3 network drivers maintainer

Add myself(Bharat) as maintainer for cxgb4 and cxgb3 network drivers.

Signed-off-by: Potnuri Bharat Teja <bharat@chelsio.com>
Link: https://lore.kernel.org/r/20240502184209.2723379-1-bharat@chelsio.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>