Update usb_read_write.py

Correct the blank line

checkbox-support/checkbox_support/scripts/usb_read_write.py

@@ -170,12 +170,12 @@ def mount_usb_storage(partition):
 
         # Unmounting the folder ignoring any "not mounted" error messages.
         subprocess.call(["umount", FOLDER_TO_MOUNT], stderr=subprocess.PIPE)
-        
+
         # Unmounting the device (e.g., "/dev/mmcblk0p1") to ensure the storage
         # device is fully detached. This prevents issues with certain
         # filesystem types like NTFS, which cannot be mounted multiple times.
         subprocess.call(["umount", device_to_mount], stderr=subprocess.PIPE)
-        
+
         # mount the target device/partition
         # if the return code of the shell command is non-zero,
         # means something wrong.