clk: samsung: s3c2443: Mark expected switch fall-through

In preparation to enabling -Wimplicit-fallthrough, mark switch
cases where we are expecting to fall through.

This patch fixes the following warnings:

drivers/clk/samsung/clk-s3c2443.c: In function ‘s3c2443_common_clk_init’:
drivers/clk/samsung/clk-s3c2443.c:390:3: warning: this statement may fall through [-Wimplicit-fallthrough=]
   samsung_clk_register_alias(ctx, s3c2450_aliases,
   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     ARRAY_SIZE(s3c2450_aliases));
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/clk/samsung/clk-s3c2443.c:393:2: note: here
  case S3C2416:
  ^~~~

Warning level 3 was used: -Wimplicit-fallthrough=3

Notice that, in this particular case,  the code comment is modified
in accordance with what GCC is expecting to find.

This patch is part of the ongoing efforts to enable
-Wimplicit-fallthrough.

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>