media: drxj: fix spelling mistake in fall-through annotations

Replace "falltrough" with a proper "fall through" annotation.

This fix is part of the ongoing efforts to enabling
-Wimplicit-fallthrough

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>