linux-firmware: update to a more recent git snapshot

This update pulls in new ath6k and realtek drivers and updates for
libertas and iwlwifi:

a707c25 Merge branch 'master' of git://dev.laptop.org/users/dsd/linux-firmware


adb6547 rtlwifi/rtl8723e: Add firmware for new driver
4e17394 linux-firmware: ath6k: add firmware for AR6004 hw1.3
bac3567 Marvell SD8787: update to v14.66.9.p96
6a08d14 Marvell SD8686: update to v9.70.20.p0
bbede96 iwlwifi: update firmware for 6205

Signed-off-by: Sven Neumann <s.neumann@raumfeld.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>