soc: qcom: pd-mapper: Fix singleton refcount

The Qualcomm pd-mapper is a refcounted singleton, but the refcount is
never incremented, which means the as soon as any remoteproc instance
stops the count will hit 0.

At this point the pd-mapper QMI service is stopped, leaving firmware
without access to the PD information. Stopping any other remoteproc
instances will result in a use-after-free, which best case manifest
itself as a refcount underflow:

  refcount_t: underflow; use-after-free.
  WARNING: CPU: 1 PID: 354 at lib/refcount.c:87 refcount_dec_and_mutex_lock+0xc4/0x148
  ...
  Call trace:
   refcount_dec_and_mutex_lock+0xc4/0x148
   qcom_pdm_remove+0x40/0x118 [qcom_pd_mapper]
   ...

Fix this by incrementing the refcount, so that the pd-mapper is only
torn down when the last remoteproc stops, as intended.

Fixes: 1ebcde047c ("soc: qcom: add pd-mapper implementation")
Signed-off-by: Bjorn Andersson <quic_bjorande@quicinc.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://lore.kernel.org/r/20240820-pd-mapper-refcount-fix-v1-1-03ea65c0309b@quicinc.com
Signed-off-by: Bjorn Andersson <andersson@kernel.org>

drivers/soc/qcom/qcom_pd_mapper.c

@@ -635,6 +635,8 @@ static int qcom_pdm_probe(struct auxiliary_device *auxdev,
 			ret = PTR_ERR(data);
 		else
 			__qcom_pdm_data = data;
+	} else {
+		refcount_inc(&__qcom_pdm_data->refcnt);
 	}
 
 	auxiliary_set_drvdata(auxdev, __qcom_pdm_data);