wifi: ath11k: Use list_count_nodes()

ath11k_wmi_fw_stats_num_vdevs() and ath11k_wmi_fw_stats_num_bcn() really
look the same as list_count_nodes(), so use the latter instead of hand
writing it.

The first ones use list_for_each_entry() and the other list_for_each(), but
they both count the number of nodes in the list.

While at it, also remove to prototypes of non-existent functions.
Based on the names and prototypes, it is likely that they should be
equivalent to list_count_nodes().

Compile tested only.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/941484caae24b89d20524b1a5661dd1fd7025492.1682542084.git.christophe.jaillet@wanadoo.fr