staging: gdm724x: Modified function name conflict set_endian

Conflict resolution for function name set_endian when building for powerpc
The name changed to gdm_set_endian

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Won Kang <wonkang@gctsemi.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>