soc: qcom: pmic_glink: Make client-lock non-sleeping

The recently introduced commit '635ce0db ("soc: qcom: pmic_glink:
don't traverse clients list without a lock")' ensured that the clients
list is not modified while traversed.

But the callback is made from the GLINK IRQ handler and as such this
mutual exclusion can not be provided by a (sleepable) mutex.

Replace the mutex with a spinlock.

Fixes: 635ce0db

 ("soc: qcom: pmic_glink: don't traverse clients list without a lock")
Signed-off-by: Bjorn Andersson <quic_bjorande@quicinc.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://lore.kernel.org/r/20240430-pmic-glink-sleep-while-atomic-v1-1-88fb493e8545@quicinc.com
Signed-off-by: Bjorn Andersson <andersson@kernel.org>