kernel-doc: ignore __printf attribute

Ignore __printf() function attributes just as other __attribute__
strings are ignored.

Fixes this kernel-doc warning message:
include/kunit/kunit-stream.h:58: warning: Function parameter or member '2' not described in '__printf'
Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Brendan Higgins <brendanhiggins@google.com>
Tested-by: Brendan Higgins <brendanhiggins@google.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

scripts/kernel-doc

@@ -1580,6 +1580,7 @@ sub dump_function($$) {
     $prototype =~ s/__must_check +//;
     $prototype =~ s/__weak +//;
     $prototype =~ s/__sched +//;
+    $prototype =~ s/__printf\s*\(\s*\d*\s*,\s*\d*\s*\) +//;
     my $define = $prototype =~ s/^#\s*define\s+//; #ak added
     $prototype =~ s/__attribute__\s*\(\(
             (?: