wifi: mwifiex: fix memory leak in mwifiex_histogram_read()

Always free the zeroed page on return from 'mwifiex_histogram_read()'.

Fixes: cbf6e055 ("mwifiex: add rx histogram statistics support")

Acked-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Dmitry Antipov <dmantipov@yandex.ru>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20230802160726.85545-1-dmantipov@yandex.ru