staging: emxx_udc: Remove unneeded cast

Fix Coccinelle alert:

drivers/staging//emxx_udc/emxx_udc.c:2689:19-21: WARNING: casting value returned by memory allocation function to (u8 *) is useless.

This issue was detected by using the Coccinelle software.

Signed-off-by: Christopher Diaz Riveros <chrisadr@gentoo.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>