Casting a pointer to an integral type doesn't require a __force
attribute, because you'll need to cast back to a pointer in order to
dereference the thing anyway.

This patch removes the redundant __force cast from __range_ok.
Reported-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>