media: meson/vdec: always init coef_node_start

It's hard for code analyzers to see that coef_node_start is
always initialized (and actually hard for humans as well!).

So change the last 'else if' to an 'else' so it is clear that
coef_node_startis always set.

This fixes a compile warning:

drivers/staging/media/meson/vdec/codec_vp9.c:1689:41: warning: 'coef_node_start' may be used uninitialized [-Wmaybe-uninitialized]
 1689 |                         coef_node_start = coef_node_start + 1;
      |                         ~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~
drivers/staging/media/meson/vdec/codec_vp9.c:1551:19: note: 'coef_node_start' was declared here
 1551 |         int node, coef_node_start, coef_count_node_start;
      |                   ^~~~~~~~~~~~~~~

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>