sched: uninline rq_clock()

uninline rq_clock() to save 263 bytes of code:

   text    data     bss     dec     hex filename
   39561    3642      24   43227    a8db sched.o.before
   39298    3642      24   42964    a7d4 sched.o.after

Signed-off-by: Ingo Molnar <mingo@elte.hu>