ata: add MAINTAINERS entry for libata PATA drivers

Add myself as the primary maintainer for libata PATA drivers.

The merging process would remain unchanged with patches going
through Tejun's tree.

Cc: Alan Cox <alan@linux.intel.com>
Cc: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Acked-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Tejun Heo <tj@kernel.org>