ztest: fix broken random call

Bad copypasta in 4d451ba, leading to random stuff being blasted all
over stack, destroying the program.

Sponsored-by: Klara, Inc.
Sponsored-by: Wasabi Technology, Inc.
Reviewed-by: Alexander Motin <alexander.motin@TrueNAS.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Igor Kozhukhov <igor@dilos.org>
Reviewed-by: Sean Eric Fagan <sean.fagan@klarasystems.com>
Signed-off-by: Rob Norris <rob.norris@klarasystems.com>
Closes #17957

Author: robn

cmd/ztest.c

@@ -8143,7 +8143,7 @@ ztest_raidz_expand_run(ztest_shared_t *zs, spa_t *spa)
 	/* Setup a 1 MiB buffer of random data */
 	uint64_t bufsize = 1024 * 1024;
 	void *buffer = umem_alloc(bufsize, UMEM_NOFAIL);
-	random_get_pseudo_bytes((uint8_t *)&buffer, bufsize);
+	random_get_pseudo_bytes((uint8_t *)buffer, bufsize);
 
 	/*
 	 * Put some data in the pool and then attach a vdev to initiate