vk_virtual_swapchain: Fix warnings caused by missing function attributes
vk_virtual_swapchain: Fix warnings caused by missing function attributes

Qining/gapid,google/agi,google/gapid,pmuetschard/gapid,Qining/gapid,Qining/gapid,pmuetschard/gapid,google/gapid,pmuetschard/gapid,pmuetschard/gapid,Qining/gapid,Qining/gapid,google/agi,pmuetschard/gapid,google/agi,Qining/gapid,pmuetschard/gapid,google/gapid,google/agi,google/agi,pmuetschard/gapid,google/gapid,google/gapid,google/gapid,google/agi,google/gapid,google/agi,pmuetschard/gapid,google/agi,google/gapid,Qining/gapid,Qining/gapid