cxgbe(4): Update firmwares to 1.26.0.0.

Changes since 1.25.6.0 are listed here. This list comes from the
Release Notes for "Chelsio Unified Wire 3.14.0.4 for Linux" dated
2021-07-08.

Fixes

BASE:

• Wait 5ms before and after the i2c command that clears the mod_select. This fixes incorrect port module type read from i2c.

Obtained from: Chelsio Communications
MFC after: 1 week
Sponsored by: Chelsio Communications