ll_rw_blk: fix gcc 4.2 warning on current_io_context()

current_io_context() is both static and exported with EXPORT_SYMBOL().
As there are no users outside of ll_rw_blk.c itself, just kill the
export.

Problem reported by Martin Michlmayr <tbm@cyrius.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

block/ll_rw_blk.c

@@ -3802,7 +3802,6 @@ static struct io_context *current_io_context(gfp_t gfp_flags, int node)
 
 	return ret;
 }
-EXPORT_SYMBOL(current_io_context);
 
 /*
  * If the current task has no IO context then create one and initialise it.