Fix typo in install-sysroot.py
Fix typo in install-sysroot.py

install-sysroot.py was intended to default to installing
the sysroot ia32, but within this script 'i386' is used to
refer to this architecture.

This most likely went unnoticed since the ia32 builder
either use branding=Official, or explicitly set
use_sysroot=1, or have a complete set of packages for
cross building on the host system.

BUG=504446

Review URL: https://codereview.chromium.org/1317973005

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#347821}

CapOM/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend