MAINTAINERS: move the befs tree to kernel.org

Update the location of the befs git tree and my email address.

Link: http://lkml.kernel.org/r/20170709110012.2991-1-luisbg@kernel.org


Signed-off-by: Luis de Bethencourt <luisbg@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>