global.h: undefine utash_fatal before re-defining
global.h: undefine utash_fatal before re-defining

Remvove compilation warning when run with 'UTASH' enabled.

Change-Id: I032613ec5704dde1674de20676144a5969a969a9
Signed-off-by: Gaëtan Harter <25db78be7c666d99eacb81d0f35148479f604823@inria.fr>

cetic/tinydtls,cetic/tinydtls,cetic/tinydtls,cetic/tinydtls