drm/msm/dsi: Fix missing put_device() call in dsi_get_phy

If of_find_device_by_node() succeeds, dsi_get_phy() doesn't
a corresponding put_device(). Thus add put_device() to fix the exception
handling.

Fixes: ec31abf6

 ("drm/msm/dsi: Separate PHY to another platform device")
Signed-off-by: Miaoqian Lin <linmq006@gmail.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://lore.kernel.org/r/20211230070943.18116-1-linmq006@gmail.com
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>