Metal: Fix a warning and compilation errors

These were oversight when developping without testing on MacOS.

source/blender/gpu/metal/mtl_shader.hh

@@ -989,6 +989,9 @@ inline bool mtl_convert_vertex_format(MTLVertexFormat shader_attrib_format,
     case GPU_COMP_I10:
       out_vert_format = MTLVertexFormatInt1010102Normalized;
       break;
+    case GPU_COMP_MAX:
+      BLI_assert_unreachable();
+      break;
   }
   *r_convertedFormat = out_vert_format;
   return (out_vert_format != MTLVertexFormatInvalid);

source/blender/gpu/metal/mtl_uniform_buffer.hh

@@ -37,6 +37,7 @@ class MTLUniformBuf : public UniformBuf {
   void bind(int slot) override;
   void bind_as_ssbo(int slot) override;
   void unbind() override;
+  void clear_to_zero() override;
 
   id<MTLBuffer> get_metal_buffer(int *r_offset);
   int get_size();

source/blender/gpu/metal/mtl_uniform_buffer.mm

@@ -84,7 +84,7 @@ void MTLUniformBuf::update(const void *data)
 void MTLUniformBuf::clear_to_zero()
 {
   /* TODO(fclem): Avoid another allocation and just do the clear on the GPU if possible. */
-  void *clear_data = calloc(size_in_bytes_);
+  void *clear_data = calloc(1, size_in_bytes_);
   this->update(clear_data);
   free(clear_data);
 }