Metal: Fix framebuffer hash ignoring sampleCount (#3140)

src/renderer_mtl.mm

@@ -3526,7 +3526,10 @@ BX_STATIC_ASSERT(BX_COUNTOF(s_accessNames) == Access::Count, "Invalid s_accessNa
 				);
 		}
 
-		murmur.add(1); // SampleCount
+		const TextureMtl &firstTexture = s_renderMtl->m_textures[_attachment[0].handle.idx];
+		const uint32_t msaaQuality = bx::uint32_satsub( (firstTexture.m_flags&BGFX_TEXTURE_RT_MSAA_MASK)>>BGFX_TEXTURE_RT_MSAA_SHIFT, 1);
+		const int32_t sampleCount = s_msaa[msaaQuality];
+		murmur.add(sampleCount);
 
 		m_pixelFormatHash = murmur.end();
 	}