ZIL: Avoid dbuf_read() in ztest_get_data()

While working on similar patches for zfs and zvol in #15153 I've
forgot about ztest.  Update it also so that we test the same code
paths as use in production.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by:	Alexander Motin <mav@FreeBSD.org>
Sponsored by:	iXsystems, Inc.
Closes #15301

cmd/ztest.c

@@ -2457,8 +2457,7 @@ ztest_get_data(void *arg, uint64_t arg2, lr_write_t *lr, char *buf,
 		zgd->zgd_lr = (struct zfs_locked_range *)ztest_range_lock(zd,
 		    object, offset, size, RL_READER);
 
-		error = dmu_buf_hold(os, object, offset, zgd, &db,
-		    DMU_READ_NO_PREFETCH);
+		error = dmu_buf_hold_noread(os, object, offset, zgd, &db);
 
 		if (error == 0) {
 			blkptr_t *bp = &lr->lr_blkptr;