This is nicer for modern R/O protection.  And noone needs it non-const, so
constify the callers as well.
Signed-off-by: NRusty Russell <rusty@rustcorp.com.au>
Signed-off-by: NAmit Shah <amit.shah@redhat.com>
To: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: linuxppc-dev@ozlabs.org
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>