fs/cifs/: fix misspellings using codespell tool

A typo is found out by codespell tool in 251th lines of cifs_swn.c:

$ codespell ./fs/cifs/
./cifs_swn.c:251: funciton  ==> function

Fix a typo found by codespell.
Signed-off-by: Liu xuzhi <liu.xuzhi@zte.com.cn>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifs/cifs_swn.c

@@ -248,7 +248,7 @@ static int cifs_swn_send_unregister_message(struct cifs_swn_reg *swnreg)
 
 /*
  * Try to find a matching registration for the tcon's server name and share name.
- * Calls to this funciton must be protected by cifs_swnreg_idr_mutex.
+ * Calls to this function must be protected by cifs_swnreg_idr_mutex.
  * TODO Try to avoid memory allocations
  */
 static struct cifs_swn_reg *cifs_find_swn_reg(struct cifs_tcon *tcon)