platform/x86/dell: alienware-wmi: Use kasprintf()

Use kasprintf() instead of hand writing it.
This saves the need of an intermediate buffer.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/f2b2c9e5d80550e480a627c1b2139d5cc9472ffa.1699775015.git.christophe.jaillet@wanadoo.fr
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>