qxl: simplify qxl_rom_size

Nowdays rom size is fixed at 8192 for live migration compat reasons.
So we can ditch the pointless math trying to calculate the size needed.
Also make the size sanity check fail at compile time not runtime.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

hw/display/qxl.c

@@ -313,9 +313,7 @@ static ram_addr_t qxl_rom_size(void)
                                  sizeof(qxl_modes);
     uint32_t rom_size = 8192; /* two pages */
 
-    required_rom_size = MAX(required_rom_size, TARGET_PAGE_SIZE);
-    required_rom_size = msb_mask(required_rom_size * 2 - 1);
-    assert(required_rom_size <= rom_size);
+    QEMU_BUILD_BUG_ON(required_rom_size > rom_size);
     return rom_size;
 }