You should not wait that long between updates.
Manjaro is a curated rolling-release distribution, which means that updates are tested longer and bundled together. So there won’t be too many updates, but then you should still update your system whenever an update becomes available.
If for whatever reason you don’t want to do this, then perhaps Manjaro is not the right distribution for you, and then you should be looking for a fixed-point-release distribution instead.
That is always a bad idea, and especially so in the middle of an update. If you interrupt an update, then you are left with a partial upgrade, and without a working kernel, because the kernel images are what gets removed at the start of the update process, and the new kernel images are installed only at the end of the update process.
Boot up from the USB stick in live mode and open up a terminal window. In this terminal window, issue the command… 
su -
Next, chroot into your installed system, like so…
manjaro-chroot -a
It will attempt to autodetect your installation. If you are presented with an output that looks like 0/0, hit 1.
Next, resume the update…
pacman-mirrors -f 5 && pacman -Syyu
mhwd-kernel -i linux54
update-grub
Now leave the chroot environment…
exit
It should be safe to reboot your system at this point.