drm/tilcdc: Fix irq free on unload

The driver only frees the reserved irq if priv->irq_enabled is set to
true. However, the driver mistakenly sets priv->irq_enabled to false,
instead of true, in tilcdc_irq_install(), and thus the driver never
frees the irq, causing issues on loading the driver a second time.

Fixes: b6366814 ("drm/tilcdc: Convert to Linux IRQ interfaces")
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Aradhya Bhatia <a-bhatia1@ti.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230919-lcdc-v1-1-ba60da7421e1@ideasonboard.com