staging: most: hdm-usb: remove reference to read function in write only macro

This patch replaces the reference to the function show_value() with
NULL in the macro MOST_DCI_WO_ATTR used for the write only attributes.
Signed-off-by: Andrey Shvetsov <andrey.shvetsov@k2l.de>
Signed-off-by: Christian Gromm <christian.gromm@microchip.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/most/hdm-usb/hdm_usb.c

@@ -952,7 +952,7 @@ static struct usb_device_id usbid[] = {
 
 #define MOST_DCI_WO_ATTR(_name) \
 	struct most_dci_attribute most_dci_attr_##_name = \
-		__ATTR(_name, S_IWUSR, show_value, store_value)
+		__ATTR(_name, S_IWUSR, NULL, store_value)
 
 /**
  * struct most_dci_attribute - to access the attributes of a dci object