[media] media-device: Remove duplicated memset() in media_enum_entities()

After the zeroing the whole struct struct media_entity_desc u_ent,
it is no longer necessary to memset(0) its u_ent.name field.

CC: stable@vger.kernel.org
Signed-off-by: Salva Peiró <speiro@ai2.upv.es>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>