initrd/gpg: add LUKS cleanup trap and fix partition derivation

- Add EXIT trap to reprovision_smartcard_from_backup() that unmounts
  /media and closes any leftover usb_mount LUKS mappings.  Error paths
  that return early after opening LUKS would otherwise leave stale
  crypto mappings, blocking subsequent USB backup drive access.
- Fix partition derivation: use sed -E s/[0-9]+$// without the (p?)
  capture group that was removing the p separator from NVMe/MMC devices
  (nvme0n1p1 -> nvme0n1, producing nvme0n12 instead of nvme0n1p2).

Signed-off-by: Thierry Laurion <insurgo@riseup.net>

Author: tlaurion

initrd/etc/gpg_functions.sh

@@ -448,6 +448,9 @@ reprovision_smartcard_from_backup() {
 	local mapper_dev parent_disk pub_partition
 	local algo_code bit_len
 
+	# Ensure LUKS mappings are cleaned up on any exit path (error or normal)
+	trap 'umount /media 2>/dev/null || true; for d in /dev/mapper/usb_mount_*; do [ -e "$d" ] && cryptsetup close "$(basename "$d")" 2>/dev/null || true; done' EXIT
+
 	# Detect dongle branding early -- needed for whiptail messages and
 	# Nitrokey Storage AES key reset in factory_reset_and_configure.
 	enable_usb