libbladeRF: Added error code return after assertion (CID 1213847)

Ensure this function can't proceed if release assertions become
disabled, and to appease static analysis tools.
libbladeRF: Fixed potential memory leak in cases with bad args  (CID 1213846)
bladeRF-cli: Fixed leak of expanded path name (CID 1206512)
bladeRF-cli: Fixed leak in case where image alloc fails (CID1206511)
bladeRF-cli: Fixed leak in TX file conversion faliure (CID 1206510)
libbladeRF: Fixed leak in FPGA flashing failure case (CID 1104234)
libbladeRF: Added "File not found" API return code

Operations that open files (e.g., firmware flash, FPGA load) now
return BLADERF_ERR_NO_FILE instead of BLADERF_ERR_IO when a file not
found. This is intended to help differentiate between user-error in the
aforementioned operations and a device-failure.
WIP: Modify the RXVGA2 calibration routines.
Calibration update.
libbladeRF: Moved LPF DC tuning value write into address loop

This is just for readability. There's no functional change, since
there's only 1 address to loop over anyway.
libbladeRF: Added register settings from LMS FAQ to DC calibration fns

The following changes have been added to lms_dc_cal_loop() and
lms_calibrate_dc(), based upon recommendations from the LMS 6002D FAQ
(version 1.0r10).

    - Use the DC_REGVAL to determine success or failure, as DC_LOCK
      is reported (in the FAQ) to be unreliable. Retry if the result is
      31, setting the count to DC_CNTVAL to 0.

    - Enable DC comparators during DC calibration (default), and
      disable them upon completion to address linearity issues.

    - Disable DACs while performing TXLPF DC calibration
bladeRF-cli: [WIP] First cut at RX DC auto calibration

Includes a workaround for convergence issues - further investigation
required. General cleanup and documentation changes still required.
bladeRF-cli: [WIP] Use fewer buffers for dc cal, start with cal at 0,0
bladeRF-cli: [WIP] Added TX DC cal operation. Further cleanup required.
bladeRF-cli: Check for divide-by-zero in interpolation function