phy: mediatek: Fix missing check in mtk_mipi_tx_probe

phy: mediatek: Fix missing check in mtk_mipi_tx_probe

[ Upstream commit 399c91c3f30531593e5ff6ca7b53f47092128669 ]

The of_device_get_match_data() function may return NULL.
Add check to prevent potential null dereference.

Signed-off-by: Miaoqian Lin <linmq006@gmail.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20211224082103.7658-1-linmq006@gmail.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>