Documentation: ubifs: Fix compression idiom

Clearly the author meant 'on the fly'.
Signed-off-by: NJoel Stanley <joel@jms.id.au>
Link: https://lore.kernel.org/r/20221005030904.65604-1-joel@jms.id.auSigned-off-by: NJonathan Corbet <corbet@lwn.net>

Documentation/filesystems/ubifs.rst

@@ -59,7 +59,7 @@ differences.
 * JFFS2 is a write-through file-system, while UBIFS supports write-back,
   which makes UBIFS much faster on writes.
 
-Similarly to JFFS2, UBIFS supports on-the-flight compression which makes
+Similarly to JFFS2, UBIFS supports on-the-fly compression which makes
 it possible to fit quite a lot of data to the flash.
 
 Similarly to JFFS2, UBIFS is tolerant of unclean reboots and power-cuts.