cifs: Fix missing credit release on failure in cifs_issue_read()

cifs: Fix missing credit release on failure in cifs_issue_read()

Fix missing release of credits in the failure path in cifs_issue_read()
lest retrying the subreq just overwrites the credits value.

Fixes: 69c3c023af25 ("cifs: Implement netfslib hooks")
Link: https://sashiko.dev/#/patchset/20260608145432.681865-1-dhowells%40redhat.com
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Paulo Alcantara (Red Hat) <pc@manguebit.org>
cc: linux-cifs@vger.kernel.org
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Steve French <stfrench@microsoft.com>