Remove redundant assignment (#14498)

Co-authored-by: Glenn Jocher <glenn.jocher@ultralytics.com>

ultralytics/nn/modules/block.py

@@ -855,7 +855,7 @@ class Attention(nn.Module):
         self.head_dim = dim // num_heads
         self.key_dim = int(self.head_dim * attn_ratio)
         self.scale = self.key_dim**-0.5
-        nh_kd = nh_kd = self.key_dim * num_heads
+        nh_kd = self.key_dim * num_heads
         h = dim + nh_kd * 2
         self.qkv = Conv(dim, h, 1, act=False)
         self.proj = Conv(dim, dim, 1, act=False)