spi: flash: use default_is_erased() to check if a block is erased

source/drivers/spi_flash.c

@@ -23,6 +23,7 @@ static struct flash_ops spi_flash_ops = {
 	.get_capacity = spi_flash_get_size,
 	.read = spi_flash_read,
 	.write = spi_flash_write,
+	.is_erased = default_flash_is_erased,
 	.erase = spi_flash_erase,
 };