[Artful SRU] Fix capsule update regression

[Manoj Iyer]

Please review and apply this patch to fix capsule update regression in 
Artful (kernel version 4.13). The patch was cleanly cherry-picked from
linus tree and tested by me on QDF2400 system. This fixes the bug
https://launchpad.net/bugs/1746019 and a test kernel is available in the
centriq PPA. https://launchpad.net/~centriq-team/+archive/ubuntu/lp1746019

This patch is critical for updating UEFI cap files on Ubuntu certified
ARM64 QDF2400 server platforms. 

Regards
Manoj Iyer