idr: Add missing __rcu annotations

Where we use the radix tree iteration macros, we need to annotate 'slot'
with __rcu.  Make sure we don't forget any new places in the future with
the same CFLAGS check used for radix-tree.c.

Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>

lib/Makefile

@@ -25,6 +25,7 @@ lib-y := ctype.o string.o vsprintf.o cmdline.o \
 	 earlycpio.o seq_buf.o nmi_backtrace.o nodemask.o win_minmax.o
 
 CFLAGS_radix-tree.o += -DCONFIG_SPARSE_RCU_POINTER
+CFLAGS_idr.o += -DCONFIG_SPARSE_RCU_POINTER
 
 lib-$(CONFIG_MMU) += ioremap.o
 lib-$(CONFIG_SMP) += cpumask.o