proc: add Alexey to MAINTAINERS

I know I'll regret it.

Link: http://lkml.kernel.org/r/20180627194840.GA18113@avx2


Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>