Fix warning in recovery.te

SELinux policy compiler complained about a quote inside the
recovery_only section of recovery.te. This section's contents are
inside quotes and thus can't contain quotes.

Test: mmm system/sepolicy produces no warnings
Bug: 33700679
Change-Id: I5bf943166f4f514d04472f7e59b025a9723eb1b8

public/recovery.te

@@ -92,7 +92,7 @@ recovery_only(`
   # Start/stop adbd via ctl.start adbd
   set_prop(recovery, ctl_default_prop)
 
-  # Read device's serial number from system properties
+  # Read serial number of the device from system properties
   get_prop(recovery, serialno_prop)
 
   # Use setfscreatecon() to label files for OTA updates.