rtc: zynqmp: initialize fract_tick

fract_tick is used uninitialized when fract_offset is 0

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Michal Simek <michal.simek@amd.com>
Link: https://lore.kernel.org/r/20220727100018.3301470-1-alexandre.belloni@bootlin.com

Author: alexandrebelloni

drivers/rtc/rtc-zynqmp.c

@@ -203,7 +203,7 @@ static int xlnx_rtc_set_offset(struct device *dev, long offset)
 	struct xlnx_rtc_dev *xrtcdev = dev_get_drvdata(dev);
 	unsigned long long rtc_ppb = RTC_PPB;
 	unsigned int tick_mult = do_div(rtc_ppb, xrtcdev->freq);
-	unsigned char fract_tick;
+	unsigned char fract_tick = 0;
 	unsigned int calibval;
 	short int  max_tick;
 	int fract_offset;