Fix a memory leak

If create_service_thread fails, we'll leak `arg`.

This fixes a static analyzer complaint:
system/core/adb/services.cpp:298:13: warning: Potential leak of memory
pointed to by 'arg'

Bug: None
Test: Reran the static analyzer. No more complaints about this leak.
Change-Id: I5aec7fd78f2cc775b650501b02bdf0039d1647ca
1 file changed