Use a cleaner test for the branch delay (BD) bit in DELAYBRANCH.

Rather than casting the value of cause to int and checking for a negative
value to determine if bit 31 is set, use a binary and with MIPS_CR_BR_DELAY.

sys/mips/mips/trap.c

@@ -281,7 +281,7 @@ struct trapdebug trapdebug[TRAPSIZE], *trp = trapdebug;
 #endif
 
 #define	KERNLAND(x)	((vm_offset_t)(x) >= VM_MIN_KERNEL_ADDRESS && (vm_offset_t)(x) < VM_MAX_KERNEL_ADDRESS)
-#define	DELAYBRANCH(x)	((int)(x) < 0)
+#define	DELAYBRANCH(x)	((x) & MIPS_CR_BR_DELAY)
 
 /*
  * MIPS load/store access type