MAINTAINERS: update rppt's email

Use my @kernel.org address

Link: https://lkml.kernel.org/r/20220203090324.3701774-1-rppt@kernel.org


Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>