wifi: ath6kl: Remove error checking for debugfs_create_dir()

It is expected that most callers should _ignore_ the errors
return by debugfs_create_dir() in ath6kl_debug_init_fs().

Signed-off-by: Wang Ming <machel@vivo.com>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/20230714014358.514-1-machel@vivo.com