package/linux-firmware: Update to 38e5405c96d10bb42b629b45210c46166461fc21

The kernel version we're using for OpenPower requests new versions of
bnx2x firmware (bnx2x-e2-7.8.19.0.fw), which are available in recent
updates to the linux-firmware package.

We also have an updated cxgb4 firmware image.

Signed-off-by: Jeremy Kerr <jk@ozlabs.org>