docs: ignore __counted_by attribute in structure definitions

kernel-doc appeared to ignore __counted_by, but appearances can be
deceiving; it caused member names to not be recognized, which manifested as
a number of spurious "Excess struct member" warnings.  Filter that
attribute out and reduce the warning onslaught slightly.

Signed-off-by: Jonathan Corbet <corbet@lwn.net>

scripts/kernel-doc

@@ -1143,6 +1143,7 @@ sub dump_struct($$) {
 	# strip attributes
 	$members =~ s/\s*$attribute/ /gi;
 	$members =~ s/\s*__aligned\s*\([^;]*\)/ /gos;
+	$members =~ s/\s*__counted_by\s*\([^;]*\)/ /gos;
 	$members =~ s/\s*__packed\s*/ /gos;
 	$members =~ s/\s*CRYPTO_MINALIGN_ATTR/ /gos;
 	$members =~ s/\s*____cacheline_aligned_in_smp/ /gos;