batman-adv: fix checkpatch warning about misspelled "cache"

commit a2d4df9b673c ("spelling.txt: add more spellings to spelling.txt")
introduced the spellcheck of "cache" for checkpatch.pl.

Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>

net/batman-adv/debugfs.c

@@ -117,7 +117,7 @@ static int batadv_bla_backbone_table_open(struct inode *inode,
 
 #ifdef CONFIG_BATMAN_ADV_DAT
 /**
- * batadv_dat_cache_open() - Prepare file handler for reads from dat_chache
+ * batadv_dat_cache_open() - Prepare file handler for reads from dat_cache
  * @inode: inode which was opened
  * @file: file handle to be initialized
  *