wifi: shell: btm_query: Fix invalid pointer cast

The 11v_btm_query shell command was calling parse_number() using
a pointer to uint8_t. This will cause memory overwrite and possible
crash. Convert to use long temporary value to avoid this.

Fix also the output prints in case of an error.

Signed-off-by: Jukka Rissanen <jukka.rissanen@nordicsemi.no>