cosmo_seq: fix post code buffer access (#2403)

Previously we could only access the first 1024 entries, now we can get
all 4096

Author: Aaron-Hartwig

drv/spartan7-loader/cosmo-seq/README.md

@@ -1,3 +1,3 @@
 FPGA images and collateral are generated from:
-[this sha](https://github.com/oxidecomputer/quartz/commit/2783ae8ea5e69f0027f4e2350211e2f99c18849c)
-[release](https://api.github.com/repos/oxidecomputer/quartz/releases/287318895)
+[this sha](https://github.com/oxidecomputer/quartz/commit/d2b888c3f36a42a172e4401a3e3d1ccabc876312)
+[release](https://api.github.com/repos/oxidecomputer/quartz/releases/291462514)