[binning] Do not use numerical operators on atomics (#539)

This fixes a comparison expression and a compound-assignment
expression that used an atomic as an operand. These should be
treated as illegal based on my understanding of the WGSL
specification (and are rejected by Tint) but Naga accepts
them and injects appropriate atomic operations during code generation.

See gfx-rs/wgpu#5474 for more details.

shader/binning.wgsl

@@ -65,14 +65,14 @@ fn main(
         atomicStore(&sh_bitmaps[i][local_id.x], 0u);
     }
     if local_id.x == 0u {
-        let failed = bump.lines > config.lines_size;
+        let failed = atomicLoad(&bump.lines) > config.lines_size;
         sh_previous_failed = u32(failed);
     }
     // also functions as barrier to protect zeroing of bitmaps
     let failed = workgroupUniformLoad(&sh_previous_failed);
     if failed != 0u {
         if global_id.x == 0u {
-            bump.failed |= STAGE_FLATTEN;
+            atomicOr(&bump.failed, STAGE_FLATTEN);
         }
         return;
     }