platform/x86: intel_telemetry_pltdrv: use devm_platform_ioremap_resource()

Use devm_platform_ioremap_resource() to simplify the code a bit.

While here, drop initialized but unused ssram_base_addr and ssram_size members.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>