media: v4l2-tpg: fix some memleaks in tpg_alloc

In tpg_alloc, resources should be deallocated in each and every
error-handling paths, since they are allocated in for statements.
Otherwise there would be memleaks because tpg_free is called only when
tpg_alloc return 0.

Fixes: 63881df9 ("[media] vivid: add the Test Pattern Generator")
Signed-off-by: Zhipeng Lu <alexious@zju.edu.cn>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>