scripts/coverity-scan/COMPONENTS.md: Fix 'char' component

scripts/coverity-scan/COMPONENTS.md: Fix 'char' component

The 'char' component:
 * includes the no-longer-present qemu-char.c, which has been
   long since split into the chardev/ backend code
 * also includes the hw/char devices

Split it into two components:
 * char is the hw/char devices
 * chardev is the chardev backends
with regexes matching our current sources.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-id: 20240604145934.1230583-3-peter.maydell@linaro.org