checkpatch: add __ro_after_init to known $Attribute

__ro_after_init is a specific __attribute__ that checkpatch does currently
not understand.

Add it to the known $Attribute types so that code that uses variables
declared with __ro_after_init are not thought to be a modifier type.

This appears as a defect in checkpatch output of code like:

static bool trust_cpu __ro_after_init = IS_ENABLED(CONFIG_RANDOM_TRUST_CPU);
[...]
       if (trust_cpu && arch_init) {

where checkpatch reports:

ERROR: space prohibited after that '&&' (ctx:WxW)
	if (trust_cpu && arch_init) {

Link: http://lkml.kernel.org/r/0fa8a2cb83ade4c525e18261ecf6cfede3015983.camel@perches.com
Signed-off-by: Joe Perches <joe@perches.com>
Reported-by: Kees Cook <keescook@chromium.org>
Tested-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

scripts/checkpatch.pl

@@ -380,6 +380,7 @@ our $Attribute	= qr{
 			__noclone|
 			__deprecated|
 			__read_mostly|
+			__ro_after_init|
 			__kprobes|
 			$InitAttribute|
 			____cacheline_aligned|