riscv, bpf: Fix incorrect runtime stats

When __bpf_prog_enter() returns zero, the s1 register is not set to zero,
resulting in incorrect runtime stats. Fix it by setting s1 immediately upon
the return of __bpf_prog_enter().

Fixes: 49b5e77ae3e2 ("riscv, bpf: Add bpf trampoline support for RV64")
Signed-off-by: Xu Kuohai <[e-mail]>
Signed-off-by: Daniel Borkmann <[e-mail]>
Reviewed-by: Pu Lehui <[e-mail]>
Acked-by: Björn Töpel <[e-mail]>
Link: https://lore.kernel.org/bpf/[e-mail]

arch/riscv/net/bpf_jit_comp64.c

···
 	if (ret)
 		return ret;
 
+	/* store prog start time */
+	emit_mv(RV_REG_S1, RV_REG_A0, ctx);
+
 	/* if (__bpf_prog_enter(prog) == 0)
 	 *	goto skip_exec_of_prog;
 	 */
 	branch_off = ctx->ninsns;
 	/* nop reserved for conditional jump */
 	emit(rv_nop(), ctx);
-
-	/* store prog start time */
-	emit_mv(RV_REG_S1, RV_REG_A0, ctx);
 
 	/* arg1: &args_off */
 	emit_addi(RV_REG_A0, RV_REG_FP, -args_off, ctx);