pseries: Update SLOF firmware image

This is a single regression fix for for 5.0:

Greg Kurz (1):
      slof: Only close stdout for virtio-serial devices

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

pc-bios/README

@@ -14,7 +14,7 @@
 - SLOF (Slimline Open Firmware) is a free IEEE 1275 Open Firmware
   implementation for certain IBM POWER hardware.  The sources are at
   https://github.com/aik/SLOF, and the image currently in qemu is
-  built from git tag qemu-slof-20200317.
+  built from git tag qemu-slof-20200327.
 
 - sgabios (the Serial Graphics Adapter option ROM) provides a means for
   legacy x86 software to communicate with an attached serial console as

SLOF @ 8e012d6f

-Subproject commit ab6984f5a6d054e1f634dda855b32e5357111974
+Subproject commit 8e012d6fddb62be833d746cef3f03e6c8beecde0