USB: gadget: gr: Re-use DEFINE_SHOW_ATTRIBUTE() macro

...instead of open coding file operations followed by custom ->open()
callbacks per each attribute.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/gadget/udc/gr_udc.c

@@ -179,8 +179,7 @@ static void gr_seq_ep_show(struct seq_file *seq, struct gr_ep *ep)
 	seq_puts(seq, "\n");
 }
 
-
-static int gr_seq_show(struct seq_file *seq, void *v)
+static int gr_dfs_show(struct seq_file *seq, void *v)
 {
 	struct gr_udc *dev = seq->private;
 	u32 control = gr_read32(&dev->regs->control);
@@ -203,19 +202,7 @@ static int gr_seq_show(struct seq_file *seq, void *v)
 
 	return 0;
 }
-
-static int gr_dfs_open(struct inode *inode, struct file *file)
-{
-	return single_open(file, gr_seq_show, inode->i_private);
-}
-
-static const struct file_operations gr_dfs_fops = {
-	.owner		= THIS_MODULE,
-	.open		= gr_dfs_open,
-	.read		= seq_read,
-	.llseek		= seq_lseek,
-	.release	= single_release,
-};
+DEFINE_SHOW_ATTRIBUTE(gr_dfs);
 
 static void gr_dfs_create(struct gr_udc *dev)
 {