[POWERPC] pseries: Avoid excess rtas_token calls

We don't need to look up the rtas event token once per
cpu per second.  This avoids some misc device-tree lookups
and string ops and so provides some minor performance
improvement.

Signed-off-by: Linas Vepstas <linas@austin.ibm.com>
----
Revised commit-log message.

 arch/powerpc/platforms/pseries/rtasd.c |   15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)
Signed-off-by: Paul Mackerras <paulus@samba.org>