ftrace: Optimize the allocation for mcount entries

If we can't allocate this size, try something smaller with half of the
size. Its order should be decreased by one instead of divided by two.

Link: https://lkml.kernel.org/r/[e-mail]

Cc: <[e-mail]>
Cc: <[e-mail]>
Cc: [e-mail]
Fixes: a79008755497d ("ftrace: Allocate the mcount record pages as groups")
Signed-off-by: Wang Wensheng <[e-mail]>
Signed-off-by: Steven Rostedt (Google) <[e-mail]>

kernel/trace/ftrace.c

···
 		/* if we can't allocate this size, try something smaller */
 		if (!order)
 			return -ENOMEM;
-		order >>= 1;
+		order--;
 		goto again;
 	}