MIPS: ptrace: Test correct task's flags in task_user_regset_view()

task_user_regset_view() should test for TIF_32BIT_REGS in the flags of
the specified task, not of the current task.

Signed-off-by: Alex Smith <alex@alex-smith.me.uk>
Cc: <stable@vger.kernel.org> # v3.13+
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/7450/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>