Revert "libbladeRF: correct RXVGA2-related bladerf_get/set_sampling methods"

This reverts commit ff5e8910d07a92ff70071e7934f8539622c47f1d.
libbladeRF: correct bladerf_set_sampling RXVGA2-related log messages

bladerf_set_sampling - for internal/external sampling, the RXVGA2
    log warning messages were reversed (enable/disable RXVGA2)