wifi: brcmfmac: wcc: Add debug messages

The message is attach and detach function are merly for debugging,
change them from pr_err to pr_debug.

Signed-off-by: Matthias Brugger <mbrugger@suse.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20230509100420.26094-1-matthias.bgg@kernel.org