usb: avoid redundant cast of kmalloc() return value in OTi-6858 driver

In drivers/usb/serial/oti6858.c::pl2303_buf_alloc() the return value
of kmalloc() is being cast to "struct pl2303_buf *", but that need
not be done here since kmalloc() returns "void *".
Signed-off-by: Jesper Juhl <jesper.juhl@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/serial/oti6858.c

@@ -1144,7 +1144,7 @@ static struct pl2303_buf *pl2303_buf_alloc(unsigned int size)
 	if (size == 0)
 		return NULL;
 
-	pb = (struct pl2303_buf *)kmalloc(sizeof(struct pl2303_buf), GFP_KERNEL);
+	pb = kmalloc(sizeof(struct pl2303_buf), GFP_KERNEL);
 	if (pb == NULL)
 		return NULL;