usb: gadget: composite: use kasprintf() instead of open coding it

Let's not reimplement generic kernel helpers,
instead call kasprintf().

[ felipe.balbi@linux.intel.com: better commit log ]
Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/gadget/composite.c

@@ -2387,18 +2387,8 @@ EXPORT_SYMBOL_GPL(usb_composite_setup_continue);
 
 static char *composite_default_mfr(struct usb_gadget *gadget)
 {
-	char *mfr;
-	int len;
-
-	len = snprintf(NULL, 0, "%s %s with %s", init_utsname()->sysname,
-			init_utsname()->release, gadget->name);
-	len++;
-	mfr = kmalloc(len, GFP_KERNEL);
-	if (!mfr)
-		return NULL;
-	snprintf(mfr, len, "%s %s with %s", init_utsname()->sysname,
-			init_utsname()->release, gadget->name);
-	return mfr;
+	return kasprintf(GFP_KERNEL, "%s %s with %s", init_utsname()->sysname,
+			 init_utsname()->release, gadget->name);
 }
 
 void usb_composite_overwrite_options(struct usb_composite_dev *cdev,