objtool, media: dib8000: Prevent divide-by-zero in dib8000_set_dds()

If dib8000_set_dds()'s call to dib8000_read32() returns zero, the result
is a divide-by-zero.  Prevent that from happening.

Fixes the following warning with an UBSAN kernel:

  drivers/media/dvb-frontends/dib8000.o: warning: objtool: dib8000_tune() falls through to next function dib8096p_cfg_DibRx()

Fixes: 173a64c ("[media] dib8000: enhancement")
Reported-by: kernel test robot <[email protected]>
Signed-off-by: Josh Poimboeuf <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Cc: Mauro Carvalho Chehab <[email protected]>
Cc: Linus Torvalds <[email protected]>
Link: https://lore.kernel.org/r/bd1d504d930ae3f073b1e071bcf62cae7708773c.1742852847.git.jpoimboe@kernel.org
Closes: https://lore.kernel.org/r/[email protected]/

Author: jpoimboe

drivers/media/dvb-frontends/dib8000.c

@@ -2701,8 +2701,11 @@ static void dib8000_set_dds(struct dib8000_state *state, s32 offset_khz)
 	u8 ratio;
 
 	if (state->revision == 0x8090) {
+		u32 internal = dib8000_read32(state, 23) / 1000;
+
 		ratio = 4;
-		unit_khz_dds_val = (1<<26) / (dib8000_read32(state, 23) / 1000);
+
+		unit_khz_dds_val = (1<<26) / (internal ?: 1);
 		if (offset_khz < 0)
 			dds = (1 << 26) - (abs_offset_khz * unit_khz_dds_val);
 		else