iwlwifi: fix TLV fragment allocation loop

In the allocation loop, "pages" will never become zero (because of the
DIV_ROUND_UP), so if we can't allocate any size and pages becomes 1,
we will keep trying to allocate 1 page until it succeeds.  And in that
case, as coverity reported, block will never be NULL.

Reported-by: coverity-bot <keescook+coverity-bot@chromium.org>
Addresses-Coverity-ID: 1487402 ("Control flow issues")
Fixes: 14124b2 ("iwlwifi: dbg_ini: implement monitor allocation flow")
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Fixes: 14124b2 ("iwlwifi: dbg_ini: implement monitor allocation flow")
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>

drivers/net/wireless/intel/iwlwifi/iwl-dbg-tlv.c

@@ -480,7 +480,14 @@ static int iwl_dbg_tlv_alloc_fragment(struct iwl_fw_runtime *fwrt,
 	if (!frag || frag->size || !pages)
 		return -EIO;
 
-	while (pages) {
+	/*
+	 * We try to allocate as many pages as we can, starting with
+	 * the requested amount and going down until we can allocate
+	 * something.  Because of DIV_ROUND_UP(), pages will never go
+	 * down to 0 and stop the loop, so stop when pages reaches 1,
+	 * which is too small anyway.
+	 */
+	while (pages > 1) {
 		block = dma_alloc_coherent(fwrt->dev, pages * PAGE_SIZE,
 					   &physical,
 					   GFP_KERNEL | __GFP_NOWARN);