MAINTAINERS: Update Albert's email, he's back at Berkeley

When I was adding a MAINTAINERS entry for SiFive's drivers I realized
that Albert's email is out of date -- he's gone back to Berkeley, so his
SiFive email is technically defunct.  This patch updates his entry to a
current email address, hosted at Berkeley.

Signed-off-by: Palmer Dabbelt <palmer@sifive.com>