cifs: change bleft in decode_unicode_ssetup back to signed type

cifs: change bleft in decode_unicode_ssetup back to signed type

BugLink: http://bugs.launchpad.net/bugs/788691

commit bfacf2225a955bea9c41c707fc72ba16009674a0 upstream.

The buffer length checks in this function depend on this value being a
signed data type, but 690c522fa converted it to an unsigned type.

Also, eliminate a problem with the null termination check in the same
function. cifs_strndup_from_ucs handles that situation correctly
already, and the existing check could potentially lead to a buffer
overrun since it increments bleft without checking to see whether it
falls off the end of the buffer.

Reported-and-Acked-by: David Howells <dhowells@redhat.com>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Steve Conklin <sconklin@canonical.com>