Fix mis-merge of intel_powerclamp.c resulting in compile error

The new intel_powerclamp thermal cooling device driver was merged in
commit 2af78448fff6 (Pull thermal management updates from Zhang Rui)
without any data conflicts.  But there was a more subtle conflict I
missed: the driver uses MAX_USER_RT_PRIO, but commit 8bd75c77b7c6
("sched/rt: Move rt specific bits into new header file") had moved that
define from <linux/sched.h> to <linux/sched/rt.h>.

Which caused this build failure:

  drivers/thermal/intel_powerclamp.c: In function ‘clamp_thread’:
  drivers/thermal/intel_powerclamp.c:360:21: error: ‘MAX_USER_RT_PRIO’ undeclared (first use in this function)
  drivers/thermal/intel_powerclamp.c:360:21: note: each undeclared identifier is reported only once for each function it appears in

And because I don't do a full "make allmodconfig" build after each pull,
I didn't notice until too late.  So now the fix is here, separately from
the merge commit.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>