ipc: Fix warning and paranoia check
In release mode, the asserts are disabled and without asserts, the variables are unused.
/home/haagch-collabora/monado/src/xrt/ipc/server/ipc_server_handler.c: In function 'ipc_handle_swapchain_create':
/home/haagch-collabora/monado/src/xrt/ipc/server/ipc_server_handler.c:721:14: warning: unused variable 'use_dedicated_allocation' [-Wunused-variable]
721 | bool use_dedicated_allocation = xscn->images[0].use_dedicated_allocation;
| ^~~~~~~~~~~~~~~~~~~~~~~~
/home/haagch-collabora/monado/src/xrt/ipc/server/ipc_server_handler.c:720:16: warning: unused variable 'size' [-Wunused-variable]
720 | size_t size = xscn->images[0].size;
| ^~~~
In addition to that, the paranoia check didn't actually use the iteration variable to check the image attributes.