Only mark fn as clean if it is clean.
This saves us from removing (prematurely added) fn from our clean set
and saves me a few percent of runtime (and misleading debugging output
from remove()).
(Bitbake rev: 884365228fcaac07421ac1440d4946693fb628c5)
Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>
Signed-off-by: Richard Purdie <rpurdie@linux.intel.com>