drm/xe: Fix devcoredump readout of IPEHR

It was reading (base) + 0x8c but that is not a valid register
and instead it should read (base) + 0x68.
So here reading the correct register and removing the wrong and
duplicated.

Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>