sched/balancing: Fix comments (trying to) refer to NOHZ_BALANCE_KICK

Fix two typos:

 - There's no such thing as 'nohz_balancing_kick', the
   flag is named 'BALANCE' and is capitalized:  NOHZ_BALANCE_KICK.

 - Likewise there's no such thing as a 'pending nohz_balance_kick'
   either, the NOHZ_BALANCE_KICK flag is all upper-case.

Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Valentin Schneider <vschneid@redhat.com>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lore.kernel.org/r/20240308105901.1096078-8-mingo@kernel.org