docs: kerneldoc.py: append the name of the parsed doc file

docs: kerneldoc.py: append the name of the parsed doc file

Finding where an error like this was generated:
	../lib/math/div64.c:73: WARNING: Duplicate C declaration, also defined in 'kernel-api'.

Can take some time, as there's no glue about what kernel-doc
tag generated it. It is a way better to display it as:

	.../Documentation/core-api/kernel-api:171: ../lib/math/div64.c:73: WARNING: Duplicate C declaration, also defined in 'kernel-api'.
	Declaration is 'div_s64_rem'.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>