Fix up libata MAINTAINERS entry

The email was botched in one entry, and I also forgot to update the
location of the git tree. It'll be under the linux-block umbrella, just
with different branches.

Reported-by: Baruch Siach <baruch@tkos.co.il>
Fixes: 7634ccd2 ("libata: maintainership update")
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>