soundwire: qcom: use consistently 'ctrl' as state variable name

The pointer to 'struct qcom_swrm_ctrl' was called sometimes 'swrm' and
sometimes 'ctrl' variable.  Choose one - 'ctrl' - so the code will be
consistent and easier to read.

No functional change.
Reviewed-by: Srinivas Kandagagatla <srinivas.kandagatla@linaro.org>
Tested-by: Srinivas Kandagagatla <srinivas.kandagatla@linaro.org>
Reviewed-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20230418095447.577001-5-krzysztof.kozlowski@linaro.orgSigned-off-by: Vinod Koul <vkoul@kernel.org>