main/postmarketos-initramfs: invalidate cached rootfs after unlock (MR 5288)

The referenced commit had surfaced a bug with the unlocking code, which
would attempt to change the output of find_root_partition while the
cached PMOS_ROOT is stale and active. Clear this variable to force
find_root_partition to find the new rootfs value.

Fixes: 7030e08e ("postmarketos-initramfs: check for root subpartition (MR 5048)")
[ci:skip-build]: already built successfully in CI

main/postmarketos-initramfs/APKBUILD

 # Maintainer: Oliver Smith <ollieparanoid@postmarketos.org>
 # Co-Maintainer: Clayton Craft <clayton@craftyguy.net>
 pkgname=postmarketos-initramfs
-pkgver=3.2.0
+pkgver=3.2.1
 pkgrel=0
 pkgdesc="Base files for the postmarketOS initramfs / initramfs-extra"
 url="https://postmarketos.org"
@@ -92,6 +92,6 @@ sha512sums="
 929a8e6cca6b2b4ac6af89fc3912e80315f51c9bf6e9479124ccb7ebe9e99c6c1cafb98d3aa01b0a76a2f6e0071ba3eb86c7a2169a15c2e1788d69458bea3471  00-initramfs-base.files
 8a4adad3785af474b36a09a05f6a3b2c4b4f43aac331a53b903abfa51ea12be1e3d1d807b7a6e66a1346815f3b0044daf8cd62e21e2dc75d2db13ee265a72985  00-initramfs-extra-base.files
 e85386077d590cd0db0745e8b58f3323a408cb6a94bca0e4395c43e4db18b0beef29324ed2bfeab6511d0e3b297c067e5a37f420a6877d9c28c285f2416ca420  init.sh
-262136623ea82d8b60432481128a2b786144ef7eae0b3759229e1a0001b5c2a16e615f3410658bfb1d87df035e204658b81d10c0a207a0de7dd84ae9e1f29e77  init_functions.sh
+e0954014d73e7a61376a2463978a4b44d17bbb2319072382a3412a8214e9c3e45266266d8eebd37634b1b18a71094055464a7c81b973501378dcf05aa5c2f4c0  init_functions.sh
 ba3275a9af788c7c782322a22a0f144d5e50e3498ea6886486a29331f23ae89cd32d500a3635cfa7cab369afba92edc18aeca64ccbf0cd589061cce23d15b46c  unudhcpd.conf
 "

main/postmarketos-initramfs/init_functions.sh

@@ -533,6 +533,7 @@ unlock_root_partition() {
 			tried=$((tried + 1))
 		done
 		ROOT_PARTITION_UNLOCKED=1
+		PMOS_ROOT=
 		# Show again the loading splashscreen
 		show_splash "Loading..."
 	fi