libvulkan: Fix count returned for incomplete wsi queries

When vkGetPhysicalDeviceSurfaceFormatsKHR,
vkGetPhysicalDevicePresentModesKHR, and vkGetSwapchainImagesKHR
returned VK_INCOMPLETE, they would overwrite the count parameter with
the number of available items, rather than the number of returned
items.

Change-Id: I6a736770f90b95ad15bfcfbe5afb4d2886817dcb
Fixes: 31490492
Test: https://gerrit.khronos.org/#/c/158/