fbdev: sm712fb: fix memory frequency by avoiding a switch/case fallthrough

A fallthrough in switch/case was introduced in f627caf55b ("fbdev:
sm712fb: fix crashes and garbled display during DPMS modesetting"),
due to my copy-paste error, which would cause the memory clock frequency
for SM720 to be programmed to SM712.

Since it only reprograms the clock to a different frequency, it's only
a benign issue without visible side-effect, so it also evaded Sudip
Mukherjee's code review and regression tests. scripts/checkpatch.pl
also failed to discover the issue, possibly due to nested switch
statements.

This issue was found by Stephen Rothwell by building linux-next with
-Wimplicit-fallthrough.

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Fixes: f627caf55b ("fbdev: sm712fb: fix crashes and garbled display during DPMS modesetting")
Signed-off-by: Yifeng Li <tomli@tomli.me>
Cc: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
Cc: "Gustavo A. R. Silva" <gustavo@embeddedor.com>
Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>

drivers/video/fbdev/sm712fb.c

@@ -898,6 +898,7 @@ static int smtc_blank(int blank_mode, struct fb_info *info)
 		case 0x712:
 			smtc_seqw(0x6a, 0x16);
 			smtc_seqw(0x6b, 0x02);
+			break;
 		case 0x720:
 			smtc_seqw(0x6a, 0x0d);
 			smtc_seqw(0x6b, 0x02);