msm: Remove extraneous ffa device check

The qsd8x50 board file contains a few references to machine_is_...
macros that are otherwise unused, and contain no machine definition.
The recent purge of unused machine definitions breaks the compilation
of this target.

Since the machine cannot ever be used, just remove the bogus checks.

Signed-off-by: David Brown <davidb@codeaurora.org>