[ELF] Linkerscript: simplify DATA_SEGMENT_ALIGN evaluation

We can simplify the evaluation of DATA_SEGMENT_ALIGN
just to simple align(). That way it will work exactly like we have in non-script case.

Change was suggested by Rafael Ávila de Espíndola

Differential revision: https://reviews.llvm.org/D22807

llvm-svn: 276745