powerpc/pseries/mce: Fix a typo in error type assignment

The error type is ICACHE not DCACHE, for case MCE_ERROR_TYPE_ICACHE.

Signed-off-by: Ganesh Goudar <ganeshgr@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210416125750.49550-1-ganeshgr@linux.ibm.com