trusty: Fix apploader short option

Fix a typo in one of the short command line options
for the Trusty application loader. The typo caused
the tool to incorrectly accept the -s short option
and ignore it, but not accept the -D option which
is the short version of --dev.

Bug: 115420908
Test: m
Change-Id: I9d03f8dd20adedbd820621ae8f9b4d13137041ed