[media] st-hva: hva_dbg_summary() should be static

As reported by gcc:

drivers/media/platform/sti/hva/hva-v4l2.c:227:6: warning: no previous prototype for 'hva_dbg_summary' [-Wmissing-prototypes]
 void hva_dbg_summary(struct hva_ctx *ctx)
      ^~~~~~~~~~~~~~~

This function is used only internally, so make it static.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>