mailmap: add entry for Mike Rapoport

Add an entry to correct my email addresses.

Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/20200708095414.12275-1-rppt@kernel.org


Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>