amt: fix typo in comment

Correct spelling on 'non-existent' in comment
Signed-off-by: Ruffalo Lavoisier <RuffaloLavoisier@gmail.com>
Link: https://lore.kernel.org/r/20220728032854.151180-1-RuffaloLavoisier@gmail.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/amt.c

@@ -449,7 +449,7 @@ static void amt_group_work(struct work_struct *work)
 	dev_put(amt->dev);
 }
 
-/* Non-existant group is created as INCLUDE {empty}:
+/* Non-existent group is created as INCLUDE {empty}:
  *
  * RFC 3376 - 5.1. Action on Change of Interface State
  *