[PATCH] hrtimers: fix possible use of NULL pointer in posix-timers

Fixup the conversion of posix-timers to hrtimers.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>