app: aboot: Fix compilation warnings in aboot.
app: aboot: Fix compilation warnings in aboot.

Fix compilation warnings in an effort to turn on WERROR.

Change-Id: I1b3dd99afd6dd6136278ab3d7b68cd441470ffa4

Foxda-Tech/polaris-bootable-bootloader-lk,CanarySolutions/little-kernel,Foxda-Tech/polaris-bootable-bootloader-lk,efidroid/lk,CanarySolutions/little-kernel,Foxda-Tech/polaris-bootable-bootloader-lk,Foxda-Tech/polaris-bootable-bootloader-lk,efidroid/lk,CanarySolutions/little-kernel,efidroid/lk,Foxda-Tech/polaris-bootable-bootloader-lk,CanarySolutions/little-kernel,efidroid/lk,CanarySolutions/little-kernel,efidroid/lk