smb: client: stop flooding dmesg in smb2_calc_signature()

[ Upstream commit a13ca780 ]

When having several mounts that share same credential and the client
couldn't re-establish an SMB session due to an expired kerberos ticket
or rotated password, smb2_calc_signature() will end up flooding dmesg
when not finding SMB sessions to calculate signatures.

Signed-off-by: Paulo Alcantara (Red Hat) <pc@manguebit.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Stable-dep-of: 343d7fe6 ("smb: client: fix use-after-free of signing key")
Signed-off-by: Sasha Levin <sashal@kernel.org>