toolchain-external: correct hash value for Linaro AArch64 toolchain source

The aarch64 Linaro toolchain source hash is not correct, probably due
to a copy/paste error. The new hash has been verified by downloading
the tarball, validating the signature, and computing the hash.

Signed-off-by: Clayton Shotwell <clayton.shotwell@rockwellcollins.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>