drivers/rtc/rtc-r9701.c: fix crash in r9701_remove()

If probing the RTC didn't succeed due to failed RTC register access, the
RTC device will be unregistered.  Then, when removing the module
r9701_remove() causes a kernel crash while trying to unregister a not
registered RTC device.  Fix this by doing RTC register access test before
RTC device registration.
Signed-off-by: NAnatolij Gustschin <agust@denx.de>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

drivers/rtc/rtc-r9701.c

@@ -125,6 +125,13 @@ static int __devinit r9701_probe(struct spi_device *spi)
 	unsigned char tmp;
 	int res;
 
+	tmp = R100CNT;
+	res = read_regs(&spi->dev, &tmp, 1);
+	if (res || tmp != 0x20) {
+		dev_err(&spi->dev, "cannot read RTC register\n");
+		return -ENODEV;
+	}
+
 	rtc = rtc_device_register("r9701",
 				&spi->dev, &r9701_rtc_ops, THIS_MODULE);
 	if (IS_ERR(rtc))
@@ -132,13 +139,6 @@ static int __devinit r9701_probe(struct spi_device *spi)
 
 	dev_set_drvdata(&spi->dev, rtc);
 
-	tmp = R100CNT;
-	res = read_regs(&spi->dev, &tmp, 1);
-	if (res || tmp != 0x20) {
-		rtc_device_unregister(rtc);
-		return res;
-	}
-
 	return 0;
 }