cifs: prevent truncation from long to int in wait_for_free_credits

[ Upstream commit 19e888678bac8c82206eb915eaf72741b2a2615c ]

The wait_event_... defines evaluate to long so we should not assign it an int as this may truncate
the value.

Reported-by: Marshall Midden <marshallmidden@gmail.com>
Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>