vkr: work around a Use-of-uninitialized-value

VkDrmFormatModifierPropertiesListEXT::drmFormatModifierCount may be used
uninitialized.  It is a codegen bug but a proper fix breaks the
protocol.  Until we are ready to finalize the protocol, let's work
around it.

It works so far because Mesa calls the function twice in a row.  In the
first call, pDrmFormatModifierProperties is NULL and the uninitialized
value is not used.  Instead, it is initialized by the host driver.

In the second call, because of how the temp pool works, the memory gets
reused and the "uninitialized value" is already initialized.  Thanks
goes to Yiwei for figuring this out.

Signed-off-by: Chia-I Wu <olvaffe@gmail.com>
Reviewed-by: Yiwei Zhang <zzyiwei@chromium.org>
Reviewed-by: Ryan Neph <ryanneph@google.com>

src/venus/venus-protocol/vn_protocol_renderer.h

@@ -1,4 +1,4 @@
-/* This file is generated by venus-protocol git-97ac37e8. */
+/* This file is generated by venus-protocol git-1117eb98. */
 
 /*
  * Copyright 2020 Google LLC

src/venus/venus-protocol/vn_protocol_renderer_device.h

@@ -6104,7 +6104,7 @@ static inline void
 vn_decode_VkDrmFormatModifierPropertiesListEXT_self_partial_temp(struct vn_cs_decoder *dec, VkDrmFormatModifierPropertiesListEXT *val)
 {
     /* skip val->{sType,pNext} */
-    /* skip val->drmFormatModifierCount */
+    /* WA1 */ val->drmFormatModifierCount = vn_peek_array_size(dec);
     if (vn_peek_array_size(dec)) {
         const uint32_t iter_count = vn_decode_array_size(dec, val->drmFormatModifierCount);
         val->pDrmFormatModifierProperties = vn_cs_decoder_alloc_temp(dec, sizeof(*val->pDrmFormatModifierProperties) * iter_count);