bladeRF-cli: Fixes for Coverity items (CID 1107236 - 1107243)

CID 1107236 - 1107238: Dismissed as being intentional/false positives

CID 1107239: Fixed overflow in check_samplerate()

CID 1107240: Fixed memory leak in tx_csv_to_sc16q12()

CID 1107241: Condition associated with defect shouldn't occur,
             as bladerf_stream_init() should never return > 0. However,
             an ETYPE_BAD has been added to the CLI error types and
             used to initialize the err_type value in the RX and TX
             tasks. ETYPE_BAD should be used to initialize
             bladerf_error_type values to default values. In the event
             that unexpected bugs occur, this may help bring them to light.

CID 1107242: Removed incorrect conditional that relied on undefined
             value of status variable.

CID 1107243: Set bladerf_stream pointer to NULL after freeing, and
             added the stream deinitialization upon failure to the
             tx code (as there was a memory leak there). The double
             free() here shouldn't be possible, as the state transitions
             don't occur as modeled. However, we should be in the
             habit of setting re-used pointer to NULL after free(),
             and we'll see if this quiets Coverity. (If not, it's
             a non-issue and we should mark it as intentional.)