sched, trace: Fix prev_state output in sched_switch tracepoint

sched, trace: Fix prev_state output in sched_switch tracepoint

commit 3f5fe9fef5b2 ("sched/debug: Fix task state recording/printout")
tried to fix the problem introduced by a previous commit efb40f588b43
("sched/tracing: Fix trace_sched_switch task-state printing"). However
the prev_state output in sched_switch is still broken.

task_state_index() uses fls() which considers the LSB as 1. Left
shifting 1 by this value gives an incorrect mapping to the task state.
Fix this by decrementing the value returned by __get_task_state()
before shifting.

Link: http://lkml.kernel.org/r/[email protected]
Cc: [email protected]
Fixes: 3f5fe9fef5b2 ("sched/debug: Fix task state recording/printout")
Signed-off-by: Pavankumar Kondeti <[email protected]>
Signed-off-by: Steven Rostedt (VMware) <[email protected]>