MIPS: vpe.c: Fix null pointer dereference in print arguments.

In the printk, the variable t euqals to NULL, so there is no t->index.
Use v->tc->index instead.

[ralf@linux-mips.org: Use opportunity of changing this line anyway to make
this line whitespacely correct.]

Signed-off-by: Cong Ding <dinggnu@gmail.com>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/4792/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>