sched: Fix string comparison in /proc/sched_features

Fix incorrect handling of the following case:

 INTERACTIVE
 INTERACTIVE_SOMETHING_ELSE

The comparison only checks up to each element's length.

Changelog since v1:
 - Embellish using some Rostedtisms.
  [ mingo:                 ^^ == smaller and cleaner ]

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Reviewed-by: Steven Rostedt <rostedt@goodmis.org>
Cc: <stable@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Tony Lindgren <tony@atomide.com>
LKML-Reference: <20100913214700.GB16118@Krystal>
Signed-off-by: Ingo Molnar <mingo@elte.hu>