MIPS: Fix BREAK code interpretation heuristics

Do not lose the other half of the BREAK code where there is an upper
half.  This is so that e.g. `BREAK 7, 7' is not interpreted as a divide
by zero trap, while `BREAK 0, 7' or `BREAK 7, 0' still are.

Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/9697/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/kernel/traps.c

@@ -943,7 +943,7 @@ asmlinkage void do_bp(struct pt_regs *regs)
 	 * We handle both cases with a simple heuristics.  --macro
 	 */
 	if (bcode >= (1 << 10))
-		bcode >>= 10;
+		bcode = ((bcode & ((1 << 10) - 1)) << 10) | (bcode >> 10);
 
 	/*
 	 * notify the kprobe handlers, if instruction is likely to