parisc: Switch do_timer() to xtime_update()

xtime_update() takes the xtime_lock itself.

Signed-off-by: Torben Hohn <torbenh@gmx.de>
Cc: hch@infradead.org
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: johnstul@us.ibm.com
Cc: Helge Deller <deller@gmx.de>
Cc: "James E.J. Bottomley" <jejb@parisc-linux.org>
Cc: Kyle McMartin <kyle@mcmartin.ca>
Cc: yong.zhang0@gmail.com
LKML-Reference: <20110127150017.23248.22559.stgit@localhost>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>