selftests: refactor the lsm `flags_overset_lsm_set_self_attr` test

Remove the temporary context variable `tctx` to simplify the code. use
the original context `ctx` directly in calls to `lsm_get_self_attr`,
eliminating redundancy without any functional changes.

Reviewed-by: Casey Schaufler <[e-mail]>
Reviewed-by: Shuah Khan <[e-mail]>
Signed-off-by: Amit Vadhavana <[e-mail]>
[PM: subject tweak]
Signed-off-by: Paul Moore <[e-mail]>

tools/testing/selftests/lsm/lsm_set_self_attr_test.c

···
 TEST(flags_overset_lsm_set_self_attr)
 {
 	const long page_size = sysconf(_SC_PAGESIZE);
-	char *ctx = calloc(page_size, 1);
+	struct lsm_ctx *ctx = calloc(page_size, 1);
 	__u32 size = page_size;
-	struct lsm_ctx *tctx = (struct lsm_ctx *)ctx;
 
 	ASSERT_NE(NULL, ctx);
 	if (attr_lsm_count()) {
-		ASSERT_LE(1, lsm_get_self_attr(LSM_ATTR_CURRENT, tctx, &size,
+		ASSERT_LE(1, lsm_get_self_attr(LSM_ATTR_CURRENT, ctx, &size,
 					       0));
 	}
-	ASSERT_EQ(-1, lsm_set_self_attr(LSM_ATTR_CURRENT | LSM_ATTR_PREV, tctx,
+	ASSERT_EQ(-1, lsm_set_self_attr(LSM_ATTR_CURRENT | LSM_ATTR_PREV, ctx,
 					size, 0));
 
 	free(ctx);