utils/getdeveloperlib.py: fix issue with hasfile()

utils/getdeveloperlib.py: fix issue with hasfile()

pkg-stats is not able anymore to set the developers for defconfigs and
packages. This issue is introduced with
ae86067a151b6596ca492d6f94ed513f4f8e18d7. The hasfile() method from
Developer object tries to check an absolute path against a relative path.

Convert the filepath to be checked also into an absolute path.

Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Heiko Thiery <heiko.thiery@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>