Use `data_x_times` instead of big u8-slice

src/epd2in9/mod.rs

@@ -200,11 +200,8 @@ where
         let color = self.background_color.get_byte_value();
 
         //TODO: this is using a big buffer atm, is it better to just loop over sending a single byte?
-        self.interface.cmd_with_data(
-            spi,
-            Command::WRITE_RAM,
-            &[color; WIDTH as usize / 8 * HEIGHT as usize]
-        )
+        self.interface.cmd(spi, Command::WRITE_RAM)?;
+        self.interface.data_x_times(spi, color, WIDTH / 8 * HEIGHT)
     }
 
     fn set_background_color(&mut self, background_color: Color) {