UBUNTU: [Packaging] build-avb: fix errors in building initrd

BugLink: https://bugs.launchpad.net/bugs/1927006



Fix path in provided for kernel modules during initrd generation
This fixes following error during initrd build:

+ ubuntu-core-initramfs create-initrd --output initrd.img --kerneldir /<<PKGBUILDDIR>>/debian/linux-image-unsigned-4.14.0-1011-signing/4.14.0-1011.11/modules/lib/modules --kernelver 4.14.0-1011-qcomm
dracut-install: ERROR: installing '/tmp/tmpjnne8193.ubuntu-core-initramfs/kernel/usr/lib/modules/4.14.0-1011-qcomm/modules.order' to 'usr/lib/modules/4.14.0-1011-qcomm/modules.order'
Traceback (most recent call last):
  File "/usr/bin/ubuntu-core-initramfs", line 222, in <module>
    main()
  File "/usr/bin/ubuntu-core-initramfs", line 218, in main
    globals()[args.subcmd.replace("-", "_")](parser, args)
  File "/usr/bin/ubuntu-core-initramfs", line 66, in create_initrd
    subprocess.check_call(
  File "/usr/lib/python3.8/subprocess.py", line 364, in check_call
    raise CalledProcessError(retcode, cmd)
subprocess.CalledProcessError: Command '['/usr/lib/dracut/dracut-install', '-D', '/tmp/tmpjnne8193.ubuntu-core-initramfs/main', '-r', '/tmp/tmpjnne8193.ubuntu-core-initramfs/kernel', '/tmp/tmpjnne8193.ubuntu-core-initramfs/kernel/usr/lib/modules/4.14.0-1011-qcomm/modules.order', 'usr/lib/modules/4.14.0-1011-qcomm/modules.order']' returned non-zero exit status 1.
make: *** [debian/rules.d/2-binary-arch.mk:243: install-qcomm] Error 1

Signed-off-by: Shrirang Bagul <shrirang.bagul@canonical.com>