ath11k: Fix the spectral minimum FFT bin count

User was not able to configure the spectral with the FFT bin count 32.
In all supported platforms, the expected minimum FFT bin count is 32 but
it was wrongly defined as 64. This restrict the user to not configure
down to the actually supported minimum FFT bin count. So update the
minimum FFT bin count as 32.

Tested-on: IPQ8074 hw2.0 AHB WLAN.HK.2.4.0.1-01492-QCAHKSWPL_SILICONZ-1
Tested-on: IPQ6018 hw1.0 AHB WLAN.HK.2.4.0.1-00330-QCAHKSWPL_SILICONZ-1

Signed-off-by: Karthikeyan Periyasamy <periyasa@codeaurora.org>
Signed-off-by: Jouni Malinen <jouni@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20210721180809.90960-4-jouni@codeaurora.org