wlan: OOB access may occur due to total numChannels exceeds max value

Out of Buffer access may occur in wmi_get_buf_extscan_start_cmd()
function if user provided inputs are different for below parameters
which are assigned in hdd_extscan_start_fill_bucket_channel_spec()
function

1. QCA_WLAN_VENDOR_ATTR_EXTSCAN_BUCKET_SPEC_NUM_CHANNEL_SPECS
2. QCA_WLAN_VENDOR_ATTR_EXTSCAN_CHANNEL_SPEC

To address this issue return failure status if numChannels is not
equal to the total number of channel entries.

Change-Id: I60d74161dc3752bd7f609af3910d7c86a99488ec
CRs-Fixed: 2349232