fs: cifs: remove unused variable.

In SMB2_set_compression(), the "res_key" variable is only initialized to NULL
and later kfreed. It is therefore useless and should be removed.

Found with the following semantic patch:

<smpl>
@@
identifier foo;
identifier f;
type T;
@@
* f(...) {
...
* T *foo = NULL;
... when forall
    when != foo
* kfree(foo);
...
}
</smpl>
Signed-off-by: Cyril Roelandt <tipecaml@gmail.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>

fs/cifs/smb2pdu.c

@@ -1352,7 +1352,6 @@ SMB2_set_compression(const unsigned int xid, struct cifs_tcon *tcon,
 		     u64 persistent_fid, u64 volatile_fid)
 {
 	int rc;
-	char *res_key = NULL;
 	struct  compress_ioctl fsctl_input;
 	char *ret_data = NULL;
 
@@ -1365,7 +1364,6 @@ SMB2_set_compression(const unsigned int xid, struct cifs_tcon *tcon,
 			2 /* in data len */, &ret_data /* out data */, NULL);
 
 	cifs_dbg(FYI, "set compression rc %d\n", rc);
-	kfree(res_key);
 
 	return rc;
 }