ksmbd: fix credit count leakage

ksmbd: fix credit count leakage

commit 84c5aa47925a1f40d698b6a6a2bf67e99617433d upstream.

This patch fix the failure from smb2.credits.single_req_credits_granted
test. When client send 8192 credit request, ksmbd return 8191 credit
granted. ksmbd should give maximum possible credits that must be granted
within the range of not exceeding the max credit to client.

Cc: stable@vger.kernel.org
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>