fsogsmd: fix +CNMA response validation
This fixes the warnings:
2013-02-06T20:25:32.676932Z [DEBUG] libfsotransport <0710:3>: Wrote '+CNMA=0'. Waiting (5s) for answer...
2013-02-06T20:25:32.692560Z [DEBUG] libfsotransport <0710:3>: SRC: "+CNMA=0" -> [ "OK" ]
2013-02-06T20:25:32.693249Z [WARN] TiCalypsoModem <4C>: Unexpected length 1 for FsoGsmPlusCNMA
2013-02-06T20:25:32.693618Z [WARN] FsoGsmAtSmsHandler <
250997500793162>: Failed to acknowledge SMS message; further SMS messa
ge handling will maybe faulty!
2013-02-06T20:25:32.694284Z [WARN] FsoGsmAtSmsHandler <
250997500793162>: Could not acknowledge incoming message
Signed-off-by: Paul Fertser <fercerpav@gmail.com>