zink: fix win32 detection in zink_device_info

str.find(substr) returns -1 if the substring's not in the string, and
bool(-1) returns True in Python, so the _WIN32 ifdef guard was actually
inserted everywhere.

Also, the win32 functions actually have "Win32" in their name, like
vkGetMemoryWin32HandleKHR

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/35389>

src/gallium/drivers/zink/zink_device_info.py

@@ -750,7 +750,7 @@ zink_verify_device_extensions(struct zink_screen *screen)
 <%helpers:guard ext="${ext}">
    if (screen->info.have_${ext.name_with_vendor()}) {
 %for cmd in registry.get_registry_entry(ext.name).device_commands:
-%if cmd.find("win32"):
+%if cmd.find("Win32") != -1:
 #ifdef _WIN32
 %endif
       if (!screen->vk.${cmd.lstrip("vk")}) {
@@ -760,7 +760,7 @@ zink_verify_device_extensions(struct zink_screen *screen)
          screen->vk.${cmd.lstrip("vk")} = (PFN_${cmd})zink_stub_function_not_loaded;
 #endif
       }
-%if cmd.find("win32"):
+%if cmd.find("Win32") != -1:
 #endif
 %endif
 %endfor