ARM: imx: flag failure of of_iomap

 imx_set_aips is assuming that the address returned from of_iomap is
valid which it probably is in the normal case - as the call site
is void error propagation is not possible but never the less at least
a WARN_ON() seems warranted here.
Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>
Fixes: commit e57e4ab5 ("ARM: i.MX: allow disabling supervisor protect via DT")
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm/mach-imx/cpu.c

@@ -68,6 +68,7 @@ void __init imx_aips_allow_unprivileged_access(
 
 	for_each_compatible_node(np, NULL, compat) {
 		aips_base_addr = of_iomap(np, 0);
+		WARN_ON(!aips_base_addr);
 		imx_set_aips(aips_base_addr);
 	}
 }