[ET-VK] Applying bias after sum calculation in conv2d pw shader to improve performance.

This diff improves the performance of the conv2d pw shader by changing the order of operations to apply bias after the sum calculation.

Differential Revision: [D75450662](https://our.internmc.facebook.com/intern/diff/D75450662/)

[ghstack-poisoned]

Author: trivedivivek

backends/vulkan/runtime/graph/ops/glsl/conv2d_pw_s1p0.glsl

@@ -79,14 +79,9 @@ void main() {
   // Tuple of consecutive 4 elements represents a single output texel.
   float sum[TILE_SIZE_X * TILE_SIZE_Y * 4];
 
-  const vec4 bias = texelFetch(t_bias, ivec2(out_pos_z, 0), 0);
-
   // Initialize the output array with the bias value
-  for (int i = 0; i < TILE_SIZE_X * TILE_SIZE_Y * 4; i += 4) {
-    sum[i] = bias.x;
-    sum[i + 1] = bias.y;
-    sum[i + 2] = bias.z;
-    sum[i + 3] = bias.w;
+  for (int i = 0; i < TILE_SIZE_X * TILE_SIZE_Y * 4; i++) {
+    sum[i] = 0;
   }
 
   int z4 = 0;
@@ -157,10 +152,13 @@ void main() {
     }
   }
 
+  const vec4 bias = texelFetch(t_bias, ivec2(out_pos_z, 0), 0);
+
   for (int i = 0; i < TILE_SIZE_X * TILE_SIZE_Y; ++i) {
     const ivec3 pos_l = ivec3(pos[i * 2], pos[i * 2 + 1], out_pos_z);
     if (all(lessThan(pos_l.xy, out_limits.xy))) {
-      imageStore(t_out, pos_l, op(vec4(sum[i * 4], sum[i * 4 + 1], sum[i * 4 + 2], sum[i * 4 + 3]), out_min, out_max));
+      const vec4 out_sum = vec4(sum[i * 4], sum[i * 4 + 1], sum[i * 4 + 2], sum[i * 4 + 3]);
+      imageStore(t_out, pos_l, op(out_sum + bias, out_min, out_max));
     }
   }
 }