[partition] Simplify space calculations

- Q_ASSERT doesn't work in constexpr functions because it's not
 - May as well calculate bytes at compile-time, no need to give
   the runaround via number-of-MiB

src/modules/partition/core/PartitionActions.cpp

@@ -83,10 +83,7 @@ swapSuggestion( const qint64 availableSpaceB )
 constexpr qint64
 alignBytesToBlockSize( qint64 bytes, qint64 blocksize )
 {
-    Q_ASSERT( bytes >= 0 );
-    Q_ASSERT( blocksize > 0 );
     qint64 blocks = bytes / blocksize;
-    Q_ASSERT( blocks >= 0 );
 
     if ( blocks * blocksize != bytes )
         ++blocks;
@@ -114,17 +111,17 @@ doAutopartition( PartitionCoreModule* core, Device* dev, const QString& luksPass
     // the logical sector size (usually 512B). EFI starts with 2MiB
     // empty and a 300MiB EFI boot partition, while BIOS starts at
     // the 1MiB boundary (usually sector 2048).
-    int uefisys_part_size = isEfi ? 300 : 0;
-    int empty_space_size = isEfi ? 2 : 1;
+    int uefisys_part_sizeB = isEfi ? 300_MiB : 0_MiB;
+    int empty_space_sizeB = isEfi ? 2_MiB : 1_MiB;
 
     // Since sectors count from 0, if the space is 2048 sectors in size,
     // the first free sector has number 2048 (and there are 2048 sectors
     // before that one, numbered 0..2047).
-    qint64 firstFreeSector = bytesToSectors( MiBtoBytes(empty_space_size), dev->logicalSize() );
+    qint64 firstFreeSector = bytesToSectors( empty_space_sizeB, dev->logicalSize() );
 
     if ( isEfi )
     {
-        qint64 efiSectorCount = bytesToSectors( MiBtoBytes(uefisys_part_size), dev->logicalSize() );
+        qint64 efiSectorCount = bytesToSectors( uefisys_part_sizeB, dev->logicalSize() );
         Q_ASSERT( efiSectorCount > 0 );
 
         // Since sectors count from 0, and this partition is created starting