lsatt: Do not print "no matches" message unconditionally.

lsatt: Do not print "no matches" message unconditionally.

com_lsatt() needs to know if output has been sent to the client in
order to decide whether it should print the "no matches" error message.
Currently this message is printed if at least one argument was given
and send_callback_request() returned zero.

However, send_callback_request() returns zero on success and negative
on errors. Hence, if at least one argument was given, the error
message is printed regardless of whether there was a match.

Fix this bug by changing send_callback_request() to return the number
of received shared memory areas on success.