unixstuff.c : fix issue where Minerva was finding real RAMTOP

This caused the RAMTOP inside vm to be the top of memory where
extended screen was instead of just below the extended screen.

Signed-off-by: Graeme Gregory <graeme@xora.org.uk>

unixstuff.c

@@ -968,7 +968,7 @@ void uqlxInit()
 	InitialSetup();
 
 	if (isMinerva) {
-		reg[1] = (RTOP & ~16383) | 1 | 2 | 4 | 16;
+		reg[1] = ((RTOP) & ~16383) | 1;
 		SetPC(0x186);
 	}