clk: Properly handle notifier return values

Notifiers may return NOTIFY_(OK|DONE|STOP|BAD). The CCF uses an
inconsistent mix of checking against NOTIFY_STOP or NOTIFY_BAD.
This inconsistency leaves errors undetected in some cases:
clk_set_parent() calls __clk_speculate_rates(), which stops when it
hits a NOTIFIER_BAD (STOP is ignored), and passes this value back to the
caller.
clk_set_parent() compares this return value against NOTIFY_STOP only,
ignoring NOTIFY_BAD returns.

Use NOTIFY_STOP_MASK to detect a negative notifier return value and
document all four return value options.

Signed-off-by: Soren Brinkmann <soren.brinkmann@xilinx.com>
Signed-off-by: Mike Turquette <mturquette@linaro.org>

include/linux/clk.h

@@ -28,16 +28,16 @@ struct clk;
  * PRE_RATE_CHANGE - called immediately before the clk rate is changed,
  *     to indicate that the rate change will proceed.  Drivers must
  *     immediately terminate any operations that will be affected by the
- *     rate change.  Callbacks may either return NOTIFY_DONE or
- *     NOTIFY_STOP.
+ *     rate change.  Callbacks may either return NOTIFY_DONE, NOTIFY_OK,
+ *     NOTIFY_STOP or NOTIFY_BAD.
  *
  * ABORT_RATE_CHANGE: called if the rate change failed for some reason
  *     after PRE_RATE_CHANGE.  In this case, all registered notifiers on
  *     the clk will be called with ABORT_RATE_CHANGE. Callbacks must
- *     always return NOTIFY_DONE.
+ *     always return NOTIFY_DONE or NOTIFY_OK.
  *
  * POST_RATE_CHANGE - called after the clk rate change has successfully
- *     completed.  Callbacks must always return NOTIFY_DONE.
+ *     completed.  Callbacks must always return NOTIFY_DONE or NOTIFY_OK.
  *
  */
 #define PRE_RATE_CHANGE			BIT(0)