platform/x86: think-lmi: Prevent underflow in index_store()

There needs to be a check to prevent negative offsets for
setting->index. I have reviewed this code and I think that the
"if (block->instance_count <= instance)" check in __query_block() will
prevent this from resulting in an out of bounds access. But it's
still worth fixing.

Fixes: 640a5fa50a42 ("platform/x86: think-lmi: Opcode support")
Signed-off-by: Dan Carpenter <[e-mail]>
Link: https://lore.kernel.org/r/20211217071209.GF26548@kili
Reviewed-by: Hans de Goede <[e-mail]>
Signed-off-by: Hans de Goede <[e-mail]>

drivers/platform/x86/think-lmi.c

···
 	if (err < 0)
 		return err;
 
-	if (val > TLMI_INDEX_MAX)
+	if (val < 0 || val > TLMI_INDEX_MAX)
 		return -EINVAL;
 
 	setting->index = val;