mamba_vision.py bug report for conv_bias

[douzsh]

conv_bias // 2 should be correct.

      self.conv1d_x = nn.Conv1d(
            in_channels=self.d_inner // 2,
            out_channels=self.d_inner // 2,
            bias=conv_bias,
            kernel_size=d_conv,
            groups=self.d_inner // 2,
            **factory_kwargs,
        )
       self.conv1d_z = nn.Conv1d(
            in_channels=self.d_inner // 2,
            out_channels=self.d_inner // 2,
            bias=conv_bias,
            kernel_size=d_conv,
            groups=self.d_inner // 2,
            **factory_kwargs,
        )