binman: drop "faked" return value from check_fake_fname

binman: drop "faked" return value from check_fake_fname

check_fake_fname sets the faked member of the entry. Use that member
to get the faked status instead of a returned value indicating the same.
Add type annotations to the modified functions while at it.

Signed-off-by: Yannic Moog <y.moog@phytec.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bryan Brattlof <bb@ti.com>