Fix typo in vdev_raidz_math.c

Fix typo in vdev_raidz_math.c

Reviewed by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: George Melikov <mail@gmelikov.ru>
Signed-off-by: Brad Forschinger <github@bnjf.id.au>
Closes #8875
Closes #8880

module/zfs/vdev_raidz_math.c

@@ -472,7 +472,7 @@ vdev_raidz_math_init(void)
 	return;
 #endif
 
-	/* Fake an zio and run the benchmark on a warmed up buffer */
+	/* Fake a zio and run the benchmark on a warmed up buffer */
 	bench_zio = kmem_zalloc(sizeof (zio_t), KM_SLEEP);
 	bench_zio->io_offset = 0;
 	bench_zio->io_size = BENCH_ZIO_SIZE; /* only data columns */