make logdrv also use int13 stub

kernel/drive.asm

@@ -42,6 +42,8 @@ dinit:		; copy previously set DPT to our data area
 		; set vector
 		mov word [4*0x1E], dpt
 		mov word [4*0x1E+2], ds
+		; set to invalid drive
+		mov byte [dsknum], 0xFF
 		ret
 
 		; int 13 stub
@@ -66,7 +68,7 @@ int13:		; debug output
 		; restore DPT to default values if possible
 		; IN	dl	bios drive number
 rstdpt:		mov ah, 8
-		int 0x13
+		call int13
 		jc .ret
 		mov ax, es
 		or ax, di
@@ -95,7 +97,7 @@ logdrv:		; dont do anything if drive already selected
 		cmp dl, [dsknum]
 		je .ret
 		; clear out current contents
-.force:		push dx
+		push dx
 		call flush
 		mov ax, 0xFFFF
 		mov [dskseek], ax