soc: qcom: llcc: Handle a second device without data corruption

Usually there is only one llcc device. But if there were a second, even
a failed probe call would modify the global drv_data pointer. So check
if drv_data is valid before overwriting it.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Fixes: a3134fb0 ("drivers: soc: Add LLCC driver")
Link: https://lore.kernel.org/r/20230926083229.2073890-1-u.kleine-koenig@pengutronix.de


Signed-off-by: Bjorn Andersson <andersson@kernel.org>