usb/langwell_udc: reset the maxpacket when disable ep

usb/langwell_udc: reset the maxpacket when disable ep

BZ: 29129

This patch resets the maxpacket value, as everytime the
ep descriptor maxpacketsize will be from ep maxpacket.
If we don't reset the maxpacket, errors will happen when
reassign eps to new gadget functions.

Change-Id: Ice22e8d4b78ba6a967cee6ce5fbecbfc79b42759
Signed-off-by: Wu, Hao <hao.wu@intel.com>
Reviewed-on: http://android.intel.com:8080/40943
Reviewed-by: Zhuang, Jin Can <jin.can.zhuang@intel.com>
Reviewed-by: Tang, Richard <richard.tang@intel.com>
Reviewed-by: Li, Wenji <wenji.li@intel.com>
Reviewed-by: Meng, Zhe <zhe.meng@intel.com>
Tested-by: Meng, Zhe <zhe.meng@intel.com>
Reviewed-by: buildbot <buildbot@intel.com>
Tested-by: buildbot <buildbot@intel.com>