rtc: Move variable into switch case statement

When building with automatic stack variable initialization, GCC 12
complains about variables defined outside of switch case statements.
Move the variable into the case that uses it, which silences the warning:

drivers/rtc/dev.c: In function 'rtc_dev_ioctl':
drivers/rtc/dev.c:394:30: warning: statement will never be executed [-Wswitch-unreachable]
  394 |                         long offset;
      |                              ^~~~~~

Fixes: 6a8af1b6 ("rtc: add parameter ioctl")
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20211209043915.1378393-1-keescook@chromium.org

drivers/rtc/dev.c

@@ -391,14 +391,14 @@ static long rtc_dev_ioctl(struct file *file,
 		}
 
 		switch(param.param) {
-			long offset;
 		case RTC_PARAM_FEATURES:
 			if (param.index != 0)
 				err = -EINVAL;
 			param.uvalue = rtc->features[0];
 			break;
 
-		case RTC_PARAM_CORRECTION:
+		case RTC_PARAM_CORRECTION: {
+			long offset;
 			mutex_unlock(&rtc->ops_lock);
 			if (param.index != 0)
 				return -EINVAL;
@@ -407,7 +407,7 @@ static long rtc_dev_ioctl(struct file *file,
 			if (err == 0)
 				param.svalue = offset;
 			break;
-
+		}
 		default:
 			if (rtc->ops->param_get)
 				err = rtc->ops->param_get(rtc->dev.parent, &param);