thermal: int340x: Add missing attribute for data rate base

Commit 473be511 ("thermal: int340x: processor_thermal: Add RFIM
driver")' added rfi_restriction_data_rate_base string, mmio details and
documentation, but missed adding attribute to sysfs.

Add missing sysfs attribute.

Fixes: 473be511 ("thermal: int340x: processor_thermal: Add RFIM driver")
Cc: 5.11+ <stable@vger.kernel.org> # v5.11+
Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>