staging: clocking-wizard: Handle invalid clk in notifier

Even though it should never happen, handle the case that the clock
notifier is called with an unexpected clock handle. This avoids the
compiler warning:
   drivers/staging/clocking-wizard/clk-xlnx-clock-wizard.c: In function 'clk_wzrd_clk_notifier':
>> drivers/staging/clocking-wizard/clk-xlnx-clock-wizard.c:99:6: warning: 'max' may be used uninitialized in this function [-Wmaybe-uninitialized]
      if (ndata->new_rate > max)
         ^

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Soren Brinkmann <soren.brinkmann@xilinx.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/clocking-wizard/clk-xlnx-clock-wizard.c

@@ -91,8 +91,10 @@ static int clk_wzrd_clk_notifier(struct notifier_block *nb, unsigned long event,
 
 	if (ndata->clk == clk_wzrd->clk_in1)
 		max = clk_wzrd_max_freq[clk_wzrd->speed_grade - 1];
-	if (ndata->clk == clk_wzrd->axi_clk)
+	else if (ndata->clk == clk_wzrd->axi_clk)
 		max = WZRD_ACLK_MAX_FREQ;
+	else
+		return NOTIFY_DONE;	/* should never happen */
 
 	switch (event) {
 	case PRE_RATE_CHANGE: