libbladeRF: bladerf_load_fpga no longer checks current FPGA status

This check was only being used to print an informational message.
However, it was supposed to be used to change the return value to
indicate the FPGA being re-loaded versus loaded.

Because the caller can check the FPGA state via
bladerf_is_fpga_configured(), this check has been pulled out, and the
interface now specifies that this functions return value only indicates
success (0) or failure (error code).