checkpatch: add __rcu as a sparse modifier

Fix "need consistent spacing around '*'" error after a __rcu sparse
annotation which was caused by the missing __rcu entry in the
checkpatch.pl internal list of sparse keywords.

Signed-off-by: Sven Eckelmann <sven@narfation.org>
Cc: Andy Whitcroft <apw@canonical.com>
Cc: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

scripts/checkpatch.pl

@@ -145,7 +145,8 @@ sub help {
 			__must_check|
 			__init_refok|
 			__kprobes|
-			__ref
+			__ref|
+			__rcu
 		}x;
 
 # Notes to $Attribute: