Update outdated assertion from zio_write_compress

As part of some internal gang block testing within Delphix
we hit the assertion removed by this patch. The assertion
was triggered by a ZIO that had two copies and was a gang
block making the following expression equal to 3:
```
MIN(zp->zp_copies + BP_IS_GANG(bp), spa_max_replication(spa))
```
and failing when we expected the above to be equal to
`BP_GET_NDVAS(bp)`.

The assertion is no longer valid since the following commit:
```
commit 14872aa
Author: Matthew Ahrens <matthew.ahrens@delphix.com>
Date:   Mon Feb 6 09:37:06 2023 -0800

  EIO caused by encryption + recursive gang
```

The above commit changed gang block headers so they can't
have more than 2 copies but the assertion in question from
this PR was never updated.

Signed-off-by: Serapheim Dimitropoulos <serapheim@delphix.com>

module/zfs/zio.c

@@ -1774,9 +1774,9 @@ zio_write_compress(zio_t *zio)
 		if (pass >= zfs_sync_pass_dont_compress)
 			compress = ZIO_COMPRESS_OFF;
 
-		/* Make sure someone doesn't change their mind on overwrites */
-		ASSERT(BP_IS_EMBEDDED(bp) || MIN(zp->zp_copies + BP_IS_GANG(bp),
-		    spa_max_replication(spa)) == BP_GET_NDVAS(bp));
+		ASSERT(BP_IS_EMBEDDED(bp) || BP_IS_GANG(bp) ||
+		    MIN(zp->zp_copies, spa_max_replication(spa))
+		    == BP_GET_NDVAS(bp));
 	}
 
 	/* If it's a compressed write that is not raw, compress the buffer. */