Mark switch cases where we are expecting to fall through.

This patch fixes the following warning (Building: arm):

sound/soc/ti/n810.c: In function ‘n810_ext_control’:
sound/soc/ti/n810.c:48:10: warning: this statement may fall through [-Wimplicit-fallthrough=]
   line1l = 1;
   ~~~~~~~^~~
sound/soc/ti/n810.c:49:2: note: here
  case N810_JACK_HP:
  ^~~~

sound/soc/ti/rx51.c: In function ‘rx51_ext_control’:
sound/soc/ti/rx51.c:57:6: warning: this statement may fall through [-Wimplicit-fallthrough=]
   hs = 1;
   ~~~^~~
sound/soc/ti/rx51.c:58:2: note: here
  case RX51_JACK_HP:
  ^~~~
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Acked-by: Jarkko Nikula <jarkko.nikula@bitmer.com>
Link: https://lore.kernel.org/r/20190729221534.GA18696@embeddedorSigned-off-by: Mark Brown <broonie@kernel.org>