hw/display: Allow vga_common_init() to return errors

hw/display: Allow vga_common_init() to return errors

The vga_common_init() function currently cannot report errors to its
caller. But in the following patch, we'd need this possibility, so
let's change it to take an "Error **" as parameter for this.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20220317083027.16688-3-thuth@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>