Removed some of the XXX_reg macros now that we are using the standard
CONTEXT86 structure everywhere.

diff --git a/msdos/int13.c b/msdos/int13.c
index 5574d47..d928de6 100644
--- a/msdos/int13.c
+++ b/msdos/int13.c
@@ -118,7 +118,7 @@
 				CX_reg(context) = 0x4f24;
 				break;
 			}
-			ES_reg(context) = 0x0000; /* FIXME: drive parameter table */
+			context->SegEs = 0x0000; /* FIXME: drive parameter table */
 			DI_reg(context) = 0x0000;
 #else
                 	AH_reg(context) = 0x01;