os-posix: cleanup: Replace perror with error_report

os-posix: cleanup: Replace perror with error_report

perror() is defined to fprintf(stderr,...).  HACKING says
fprintf(stderr,...) is wrong.  So perror() is too.

Signed-off-by: Ian Jackson <[email protected]>
CC: Paolo Bonzini <[email protected]>
CC: Markus Armbruster <[email protected]>
CC: Daniel P. Berrange <[email protected]>
CC: Michael Tokarev <[email protected]>
CC: Alistair Francis <[email protected]>
Reviewed-by: Philippe Mathieu-Daudé <[email protected]>
Reviewed-by: Alistair Francis <[email protected]>