efi_selftest: fix guid comparison

The `loaded image' efi selftest is comparing protocol GUIDs with the wrong
polarity.
This can be verified on the sandbox, where two protocols GUIDs are
retrieved by the test from the image handle in the following order:

1. Loaded Image Device Path Protocol GUID
2. Loaded Image Protocol GUID

The test matches on the first GUID, while it is in fact looking for the
second one; fix the comparison polarity.

Fixes: efe79a7c0de0 ("efi_selftest: test for loaded image protocol")
Signed-off-by: Vincent Stehlé <vincent.stehle@arm.com>
Cc: Heinrich Schuchardt <xypron.glpk@gmx.de>
Cc: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Cc: Tom Rini <trini@konsulko.com>
Cc: Alexander Graf <agraf@csgraf.de>
Reviewed-by: Heinrich Schuchardt <xypron.glpk@gmx.de>