[SETUPLIB] Add two hacks in partlist.c for temporarily setting consistently the disk partition style.

Add two hacks in UpdateDiskLayout() and WritePartitions() so that the
disk partition style is consistently set to a known value MBR, especially
when that disk was previously new and uninitialized (RAW).
A proper fix will be developed later when support for GPT is added.

base/setup/lib/utils/partlist.c

@@ -2881,6 +2881,9 @@ UpdateDiskLayout(
         }
     }
 
+    // HACK: See the FIXMEs in WritePartitions(): (Re)set the PartitionStyle to MBR.
+    DiskEntry->DiskStyle = PARTITION_STYLE_MBR;
+
     DiskEntry->Dirty = TRUE;
 
 #ifdef DUMP_PARTITION_TABLE
@@ -3926,6 +3929,9 @@ WritePartitions(
     // DiskEntry->NoMbr was TRUE (instead of NewDisk).
     //
 
+    // HACK: Parts of FIXMEs described above: (Re)set the PartitionStyle to MBR.
+    DiskEntry->DiskStyle = PARTITION_STYLE_MBR;
+
     /* The layout has been successfully updated, the disk is not dirty anymore */
     DiskEntry->Dirty = FALSE;