atomic: Update MAINTAINERS

Update the files list to include refcount.h and the Documentation/
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>

MAINTAINERS

@@ -2982,6 +2982,8 @@ L:	linux-kernel@vger.kernel.org
 S:	Maintained
 F:	arch/*/include/asm/atomic*.h
 F:	include/*/atomic*.h
+F:	include/linux/refcount.h
+F:	Documentation/atomic_*.txt
 F:	scripts/atomic/
 
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