media: dvb-core: fix a memory leak bug

In dvb_create_media_entity(), 'dvbdev->entity' is allocated through
kzalloc(). Then, 'dvbdev->pads' is allocated through kcalloc(). However, if
kcalloc() fails, the allocated 'dvbdev->entity' is not deallocated, leading
to a memory leak bug. To fix this issue, free 'dvbdev->entity' before
returning -ENOMEM.

Signed-off-by: Wenwen Wang <wenwen@cs.uga.edu>
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>