riscv: kprobes: Remove redundant kprobe_step_ctx

Inspired by commit ba090f9c

 ("arm64: kprobes: Remove redundant
kprobe_step_ctx"), the ss_pending and match_addr of kprobe_step_ctx
are redundant because those can be replaced by KPROBE_HIT_SS and
&cur_kprobe->ainsn.api.insn[0] + GET_INSN_LENGTH(cur->opcode)
respectively.

Remove the kprobe_step_ctx to simplify the code.

Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>