MIPS: uprobes: remove incorrect set_orig_insn

MIPS: uprobes: remove incorrect set_orig_insn

Generic kernel code implements a weak version of set_orig_insn that
moves cached 'insn' from arch_uprobe to the original code location when
the trap is removed.
MIPS variant used arch_uprobe->orig_inst which was never initialised
properly, so this code only inserted a nop instead of the original
instruction. With that change orig_inst can also be safely removed.

Signed-off-by: Marcin Nowakowski <marcin.nowakowski@imgtec.com>
Fixes: 40e084a506eb ('MIPS: Add uprobes support.')
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/14299/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>