Staging: gdm724x: Remove confusing macro gdm_lte_sdu_send in gdm_lte.c

This patch removes confusing macro gdm_lte_sdu_send as stated in TODO list
in file gdm_lte.c. It then fixes the place where the macro is used.

Signed-off-by: Rashika Kheria <rashika.kheria@gmail.com>
Reviewed-by: Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>