xtensa: Change mail addresses of Hannes Weiner and Oskar Schirmer

These old mail addresses dont exist any more.
This changes all occurences to the authors' current addresses.

Signed-off-by: Oskar Schirmer <oskar@scara.com>
Cc: Chris Zankel <chris@zankel.net>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>