posix-timers: Remove useless res field from k_clock

The res member of kclock is only used by mmtimer.c, but even there it
contains redundant information. Remove the field and fixup mmtimer.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: John Stultz <johnstul@us.ibm.com>
Tested-by: Richard Cochran <richard.cochran@omicron.at>
LKML-Reference: <20110201134418.808714587@linutronix.de>