Do not cache volume id in variable

The PARTUUID code was originally written for the boot-from-USB
scenario in which only one disk is used.
In that situation it made sense to retrieve the volume id of
the disk once, and cache it in a variable.

However in the boot from SD card, root on USB drive scenario
different drives are used, so this doesn't work.

Author: maxnet

recovery/multiimagewritethread.cpp

@@ -1007,14 +1007,16 @@ QByteArray MultiImageWriteThread::getDiskId(const QString &device)
 
 QByteArray MultiImageWriteThread::getPartUUID(const QString &devpart)
 {
-    if (_diskId.isEmpty())
-        _diskId = getDiskId(_drive);
-
-    QByteArray r = "PARTUUID="+_diskId;
+    QByteArray r;
 
     QRegExp partnrRx("([0-9]+)$");
     if (partnrRx.indexIn(devpart) != -1)
     {
+        QString drive = devpart.left(partnrRx.pos());
+        if (drive.endsWith("p"))
+            drive.chop(1);
+
+        r = "PARTUUID="+getDiskId(drive);
         int partnr = partnrRx.cap(1).toInt();
         QByteArray partnrstr = QByteArray::number(partnr, 16).rightJustified(2, '0');
         r += '-'+partnrstr;

recovery/multiimagewritethread.h

@@ -41,7 +41,6 @@ class MultiImageWriteThread : public QThread
     QString _drive, _bootdrive;
     int _extraSpacePerPartition, _sectorOffset, _part;
     QVariantList installed_os;
-    QByteArray _diskId;
     bool _multiDrives;
 
 signals: