media: MAINTAINERS: hantro: Fix typo in a filepath

Fix typo (s/platform//) in the directory path.

Cc: Ezequiel Garcia <ezequiel@collabora.com>
Cc: Philipp Zabel <p.zabel@pengutronix.de>
Fixes: a29add8c

 ("media: rockchip/vpu: rename from rockchip to hantro")
Signed-off-by: Denis Efremov <efremov@linux.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>