The system should still be bootable if you edit your Manjaro boot entry in grub (press e in grub menu) and adjust the initrd line from
initrd /boot/intel-ucode.img /boot/initramfs-5.4-x86_64.img
to
initrd /boot/initramfs-5.4-x86_64.img
and then press f10 to boot this edited entry.
Reinstall the package or at least update-grub to get a bootable system.