firewire: ohci: fix compilation on arches without PAGE_KERNEL_RO

PAGE_KERNEL_RO is not available on all architectures, so its use
in the new AR code broke compilation on sparc64.

Because the read-only mapping was just a debugging aid, just use
PAGE_KERNEL instead.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>

James Bottomley wrote:
> On Thu, 2011-01-13 at 08:27 +0100, Clemens Ladisch wrote:
>> firewire: ohci: fix compilation on arches without PAGE_KERNEL_RO, e.g. sparc
>>
>> PAGE_KERNEL_RO is not available on all architectures, so its use in the
>> new AR code broke compilation on sparc64.
>>
>> Because the R/O mapping is only used to catch drivers that try to write
>> to the reception buffer and not actually required for correct operation,
>> we can just use a normal PAGE_KERNEL mapping where _RO is not available.
[...]
>> +/*
>> + * For archs where PAGE_KERNEL_RO is not supported;
>> + * mapping the AR buffers readonly for the CPU is just a debugging aid.
>> + */
>> +#ifndef PAGE_KERNEL_RO
>> +...