simpleperf: Fix OPT_STRING_AFTER_EQUAL parsing at the end of args

When the option of type OPT_STRING_AFTER_EQUAL is at the end of
args, simpleperf wrongly reports error:
  No argument following <> option.

Bug: 343557442
Test: run simpleperf_unit_test
Change-Id: I8a6ec1e6110802de116185b04b94db144ff70335
2 files changed