kernel-doc: include line numbers for function prototypes

This should solve bad error reports like this one:

	./include/linux/iio/iio.h:0: WARNING: Unknown target name: "devm".

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/56eed0ba50cd726236acd12b11b55ce54854c5ea.1599660067.git.mchehab+huawei@kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
diff --git a/scripts/kernel-doc b/scripts/kernel-doc
index d1b4456..3982d47 100755
--- a/scripts/kernel-doc
+++ b/scripts/kernel-doc
@@ -1594,6 +1594,8 @@
     my $file = shift;
     my $noret = 0;
 
+    print_lineno($.);
+
     $prototype =~ s/^static +//;
     $prototype =~ s/^extern +//;
     $prototype =~ s/^asmlinkage +//;