cifs: Return correct error code from smb2_get_enc_key

Avoid a warning if the error percolates back up:

[440700.376476] CIFS VFS: \\otters.example.com crypt_message: Could not get encryption key
[440700.386947] ------------[ cut here ]------------
[440700.386948] err = 1
[440700.386977] WARNING: CPU: 11 PID: 2733 at /build/linux-hwe-5.4-p6lk6L/linux-hwe-5.4-5.4.0/lib/errseq.c:74 errseq_set+0x5c/0x70
...
[440700.397304] CPU: 11 PID: 2733 Comm: tar Tainted: G           OE     5.4.0-70-generic #78~18.04.1-Ubuntu
...
[440700.397334] Call Trace:
[440700.397346]  __filemap_set_wb_err+0x1a/0x70
[440700.397419]  cifs_writepages+0x9c7/0xb30 [cifs]
[440700.397426]  do_writepages+0x4b/0xe0
[440700.397444]  __filemap_fdatawrite_range+0xcb/0x100
[440700.397455]  filemap_write_and_wait+0x42/0xa0
[440700.397486]  cifs_setattr+0x68b/0xf30 [cifs]
[440700.397493]  notify_change+0x358/0x4a0
[440700.397500]  utimes_common+0xe9/0x1c0
[440700.397510]  do_utimes+0xc5/0x150
[440700.397520]  __x64_sys_utimensat+0x88/0xd0

Fixes: 61cfac6 ("CIFS: Fix possible use after free in demultiplex thread")
Signed-off-by: Paul Aurich <[email protected]>
CC: [email protected]
Signed-off-by: Steve French <[email protected]>

Author: darkrain42

fs/cifs/smb2ops.c

@@ -4285,7 +4285,7 @@ smb2_get_enc_key(struct TCP_Server_Info *server, __u64 ses_id, int enc, u8 *key)
 	}
 	spin_unlock(&cifs_tcp_ses_lock);
 
-	return 1;
+	return -EAGAIN;
 }
 /*
  * Encrypt or decrypt @rqst message. @rqst[0] has the following format: