bpf: Remove set but not used variable 'dst_known'

Fixes gcc '-Wunused-but-set-variable' warning:

kernel/bpf/verifier.c:5603:18: warning: variable ‘dst_known’
set but not used [-Wunused-but-set-variable], delete this
variable.
Signed-off-by: Mao Wenan <maowenan@huawei.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Song Liu <songliubraving@fb.com>
Link: https://lore.kernel.org/bpf/20200418013735.67882-1-maowenan@huawei.com

kernel/bpf/verifier.c

@@ -5609,7 +5609,7 @@ static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env,
 {
 	struct bpf_reg_state *regs = cur_regs(env);
 	u8 opcode = BPF_OP(insn->code);
-	bool src_known, dst_known;
+	bool src_known;
 	s64 smin_val, smax_val;
 	u64 umin_val, umax_val;
 	s32 s32_min_val, s32_max_val;
@@ -5631,7 +5631,6 @@ static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env,
 
 	if (alu32) {
 		src_known = tnum_subreg_is_const(src_reg.var_off);
-		dst_known = tnum_subreg_is_const(dst_reg->var_off);
 		if ((src_known &&
 		     (s32_min_val != s32_max_val || u32_min_val != u32_max_val)) ||
 		    s32_min_val > s32_max_val || u32_min_val > u32_max_val) {
@@ -5643,7 +5642,6 @@ static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env,
 		}
 	} else {
 		src_known = tnum_is_const(src_reg.var_off);
-		dst_known = tnum_is_const(dst_reg->var_off);
 		if ((src_known &&
 		     (smin_val != smax_val || umin_val != umax_val)) ||
 		    smin_val > smax_val || umin_val > umax_val) {