Fix some compilation warnings.

Author: https://github.com/awesomekling
Commit: https://github.com/SerenityOS/serenity/commit/7ce15f1c54c

Kernel/IDEDiskDevice.cpp

@@ -116,10 +116,8 @@ void IDEDiskDevice::handle_irq()
 
 void IDEDiskDevice::initialize()
 {
-    byte status;
-
-    status = IO::in8(IDE0_STATUS);
 #ifdef DISK_DEBUG
+    byte status = IO::in8(IDE0_STATUS);
     kprintf("initial status: ");
     print_ide_status(status);
 #endif

Kernel/ProcFS.cpp

@@ -109,6 +109,7 @@ static inline InodeIdentifier to_parent_id(const InodeIdentifier& identifier)
     case PDI_PID_fd:
         return to_identifier(identifier.fsid(), PDI_PID, to_pid(identifier), FI_PID_fd);
     }
+    ASSERT_NOT_REACHED();
 }
 
 #if 0

Kernel/Scheduler.cpp

@@ -12,13 +12,14 @@ static dword time_slice_for(Process::Priority priority)
 {
     // One time slice unit == 1ms
     switch (priority) {
-    case Process::LowPriority:
-        return 5;
-    case Process::NormalPriority:
-        return 15;
     case Process::HighPriority:
         return 50;
+    case Process::NormalPriority:
+        return 15;
+    case Process::LowPriority:
+        return 5;
     }
+    ASSERT_NOT_REACHED();
 }
 
 Process* current;

SharedGraphics/Painter.cpp

@@ -282,7 +282,6 @@ void Painter::blit(const Point& position, const GraphicsBitmap& source, const Re
     const int first_row = clipped_rect.top() - dst_rect.top();
     const int last_row = clipped_rect.bottom() - dst_rect.top();
     const int first_column = clipped_rect.left() - dst_rect.left();
-    const int last_column = clipped_rect.right() - dst_rect.left();
     RGBA32* dst = m_target->scanline(clipped_rect.y()) + clipped_rect.x();
     const RGBA32* src = source.scanline(src_rect.top() + first_row) + src_rect.left() + first_column;
     const size_t dst_skip = m_target->width();

WindowServer/WSWindow.cpp

@@ -69,6 +69,7 @@ static GUI_MouseButton to_api(MouseButton button)
     case MouseButton::Right: return GUI_MouseButton::Right;
     case MouseButton::Middle: return GUI_MouseButton::Middle;
     }
+    ASSERT_NOT_REACHED();
 }
 
 void WSWindow::on_message(WSMessage& message)