postmarketos-initramfs: fix partition cmdline priority (MR 4487)

The "pmos_[br]oot(_uuid)?" kernel cmdline args can be used to specify
how to mount the root and boot partitions. During a previous rework, the
behaviour of these was made inconsistent (becoming dependent on the
order they were specified on the cmdline).

Undo the previous "optimisation" by splitting them back out into two
FOR loops, where the _uuid variants take precedence.

main/postmarketos-initramfs/init_functions.sh

@@ -181,15 +181,20 @@ find_root_partition() {
 					break
 				fi
 			fi
-			if ! [ "$x" = "${x#pmos_root=}" ]; then
-				path="${x#pmos_root=}"
-				if [ -e "$path" ]; then
-					PMOS_ROOT="$path"
-					break
-				fi
-			fi
 		done
 
+		if [ -z "$PMOS_ROOT" ]; then
+			for x in $(cat /proc/cmdline); do
+				if ! [ "$x" = "${x#pmos_root=}" ]; then
+					path="${x#pmos_root=}"
+					if [ -e "$path" ]; then
+						PMOS_ROOT="$path"
+						break
+					fi
+				fi
+			done
+		fi
+
 		# On-device installer: before postmarketOS is installed,
 		# we want to use the installer partition as root. It is the
 		# partition behind pmos_root. pmos_root will either point to
@@ -244,18 +249,25 @@ find_boot_partition() {
 				PMOS_BOOT="$path"
 				break
 			fi
-		elif ! [ "$x" = "${x#pmos_boot=}" ]; then
-			# If the boot partition is specified explicitly
-			# then we need to check if it's a valid path, and
-			# fall back if not...
-			path="${x#pmos_boot=}"
-			if [ -e "$path" ]; then
-				PMOS_BOOT="$path"
-				break
-			fi
 		fi
 	done
 
+	if [ -z "$PMOS_BOOT" ]; then
+		# shellcheck disable=SC2013
+		for x in $(cat /proc/cmdline); do
+			if ! [ "$x" = "${x#pmos_boot=}" ]; then
+				# If the boot partition is specified explicitly
+				# then we need to check if it's a valid path, and
+				# fall back if not...
+				path="${x#pmos_boot=}"
+				if [ -e "$path" ]; then
+					PMOS_BOOT="$path"
+					break
+				fi
+			fi
+		done
+	fi
+
 	# Finally fall back to findfs by label
 	if [ -z "$PMOS_BOOT" ]; then
 		# * "pmOS_i_boot" installer boot partition (fits 11 chars for fat32)