p8chip: Restore RAS_MODE_REG to original value
p8chip: Restore RAS_MODE_REG to original value

This correctly restores the MR_THREAD_IN_DEBUG bit rather than always
clearing it after.

Signed-off-by: Michael Neuling <7b0ab45a730e48a69239010b5b8fe5fa4e8eaac6@neuling.org>

open-power/pdbg,open-power/pdbg,open-power/pdbg