soc: qcom: llcc: Use guards for mutex handling

soc: qcom: llcc: Use guards for mutex handling

Replacing manual lock/unlock pairs with guard() removes the need to
think about unlocking entirely and keeps the function trivially
structured.

Signed-off-by: Unnathi Chalicheemala <unnathi.chalicheemala@oss.qualcomm.com>
Signed-off-by: Francisco Munoz Ruiz <francisco.ruiz@oss.qualcomm.com>
Reviewed-by: Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>
Link: https://lore.kernel.org/r/20260305-external_llcc_changes1set-v1-2-6347e52e648e@oss.qualcomm.com
Signed-off-by: Bjorn Andersson <andersson@kernel.org>