sched/wait: Suppress Sparse 'variable shadowing' warning

This warning seems to show up a lot now, since ___wait_event()
is (indirectly) used inside wait_event_timeout(), which also
has a variable called __ret. Rename the one in ___wait_event()
to ___ret (another leading underscore) to suppress the warning.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/1391704121.12789.20.camel@jlt4.sipsolutions.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>