u-boot: replace AUTOREV by the linux4sam_5.5 commit ID
u-boot: replace AUTOREV by the linux4sam_5.5 commit ID

This would allow to build Yocto Project distributions on a machine without
Internet connexion.

Signed-off-by: Nicolas Ferre <45b517be0e5ec6dc3a39715767c1d18e090d39b4@microchip.com>

linux4sam/meta-atmel,linux4sam/meta-atmel,alexandrebelloni/meta-atmel,linux4sam/meta-atmel,linux4sam/meta-atmel,linux4sam/meta-atmel,alexandrebelloni/meta-atmel,alexandrebelloni/meta-atmel