sched/fair: Remove duplicate code from can_migrate_task()

Combine two branches which do the same.

Signed-off-by: Kirill Tkhai <ktkhai@parallels.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/20140922183612.11015.64200.stgit@localhost
Signed-off-by: Ingo Molnar <mingo@kernel.org>