drm/panel: boe-th101mb31ig002-28a: Fix compilation build

drm/panel: boe-th101mb31ig002-28a: Fix compilation build

Commit 77dcbce63779 ("panel/th101mb31ig002-28a: Use refcounted
allocation in place of devm_kzalloc()") switched from a kmalloc +
drm_panel_init call to a devm_drm_panel_alloc one.

However, the variable it was storing the allocated pointer in doesn't
exist, resulting in a compilation breakage.

Fixes: 77dcbce63779 ("panel/th101mb31ig002-28a: Use refcounted allocation in place of devm_kzalloc()")
Signed-off-by: Maxime Ripard <mripard@kernel.org>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Tested-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://lore.kernel.org/r/20250408122008.1676235-2-mripard@kernel.org
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>