pata_at91: fix resource release

Julias Lawall discovered that pata_at91 wasn't freeing a memory region
allocated with kzalloc() on init failure paths.  Upon review,
pata_at91 also seems to be doing unnecessary explicit resource
releases for managed resources too.  Convert memory allocation to
managed one and drop unnecessary explicit resource releases.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Julia Lawall <julia@diku.dk>
Cc: Sergey Matyukevich <geomatsi@gmail.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>