VAX780, VAX8600: Fixed bad test for UBA intr level (COVERITY)

IPL_UBA already has the subtract built in:

So it shouldn't be extracted again.

The whole routine looks a little strange, but the way it works is
that an interrupt from the UBA itself sets <bit 31> in the returned vector.
Because the vector is read by code and not used by hardware, the flag
bit is "harmless."

UBA interrupts occur only under strange circumstances, like bad map
pages and device NXMs. Under the simulator, with a debugged OS, they
never happen.

VAX/vax780_uba.c

@@ -1,6 +1,6 @@
 /* vax780_uba.c: VAX 11/780 Unibus adapter
 
-   Copyright (c) 2004-2012, Robert M Supnik
+   Copyright (c) 2004-2017, Robert M Supnik
 
    Permission is hereby granted, free of charge, to any person obtaining a
    copy of this software and associated documentation files (the "Software"),
@@ -25,6 +25,7 @@
 
    uba                  DW780 Unibus adapter
 
+   13-Mar-17    RMS     Fixed bad test for UBA intr level (COVERITY)
    25-Mar-12    RMS     Added parameter to int_ack prototype (Mark Pizzolata)
    19-Nov-08    RMS     Moved I/O support routines to I/O library
    28-May-08    RMS     Inlined physical memory routines
@@ -582,7 +583,7 @@ int32 uba_get_ubvector (int32 lvl)
 int32 i, vec;
 
 vec = 0;
-if ((lvl == (IPL_UBA - IPL_HMIN)) && uba_int) {         /* UBA lvl, int? */
+if ((lvl == IPL_UBA) && uba_int) {                      /* UBA lvl, int? */
     vec = UBA_UVEC;                                     /* set flag */
     uba_int = 0;                                        /* clear int */
     }