[IA64] fix compilation warning in sys32_epoll_wait()

This gets rid of an unused variable `error' in sys_ia32.c:sys32_epoll_wait()

Getting rid of this one makes parsing the output of the kernecomp
autobuild easier --- searching for `Error' to find a problem kept
hitting this one, even though it's only a warning.

Signed-off-by: Tony Luck <tony.luck@intel.com>