video: fbdev: lxfb_ops: Fix fall-through warnings for Clang

In preparation to enable -Wimplicit-fallthrough for Clang, fix a warning
by explicitly adding a break statement instead of letting the code fall
through to the next case.

Link: https://github.com/KSPP/linux/issues/115
Signed-off-by: Gustavo A. R. Silva <[e-mail]>
Signed-off-by: Sam Ravnborg <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/9c[e-mail]

drivers/video/fbdev/geode/lxfb_ops.c

···
 		case DC_DV_CTL:
 			/* set all ram to dirty */
 			write_dc(par, i, par->dc[i] | DC_DV_CTL_CLEAR_DV_RAM);
+			break;
 
 		case DC_RSVD_1:
 		case DC_RSVD_2: