SUNRPC: Fix a compile warning for cmpxchg64()

[ Upstream commit e732f4485a150492b286f3efc06f9b34dd6b9995 ]
Signed-off-by: NTrond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: NSasha Levin <sashal@kernel.org>

net/sunrpc/auth_gss/gss_krb5_seal.c

@@ -63,6 +63,7 @@
 #include <linux/sunrpc/gss_krb5.h>
 #include <linux/random.h>
 #include <linux/crypto.h>
+#include <linux/atomic.h>
 
 #if IS_ENABLED(CONFIG_SUNRPC_DEBUG)
 # define RPCDBG_FACILITY        RPCDBG_AUTH