dfu: select HASH

The DFU code relies on the HASH config option. Make sure it is always there
by selecting it.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Reviewed-by: Jagan Teki <jagan@openedev.com>
diff --git a/drivers/dfu/Kconfig b/drivers/dfu/Kconfig
index 56a98f5..fa27efb 100644
--- a/drivers/dfu/Kconfig
+++ b/drivers/dfu/Kconfig
@@ -2,6 +2,7 @@
 
 config USB_FUNCTION_DFU
 	bool
+	select HASH
 
 if CMD_DFU
 config DFU_TFTP