Bluetooth: Host: df: Uninitialized variable used to assign length of antenna identifiers

[ppryga-nordic]

Describe the bug
Wrong variable is used to assign length of antenna identifiers for CTE reception in AoA mode.
The variable used is cp->switch_pattern_len pointer instead of function argument params->num_ant_ids.

To Reproduce
Steps to reproduce the behavior:

1. Build direction_finding_connectionless_rx sample for nRF53 and run on the device.
2. When synchronized with periodic advertising, the CTE reception is enabled. Controller stops responding for messages due to wrong length of the HCI command.
3. Host asserts due to lack of response from Controller.

Expected behavior
CTE is successfully received and reported to Host. Controller is still responsive.

Impact
DF samples are not usable.