hwspinlock: qcom: avoid uninitialized struct members

hwspinlock: qcom: avoid uninitialized struct members

The reg_field is allocated on stack, so using the REG_FIELD macro will
ensure that unused members do not have uninitialized values.

Fixes: 19a0f61224d2 ("hwspinlock: qcom: Add support for Qualcomm HW Mutex block")
Link: https://sashiko.dev/#/patchset/20260319105947.6237-1-wsa%2Brenesas%40sang-engineering.com
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>
Link: https://lore.kernel.org/r/20260512091339.31085-2-wsa+renesas@sang-engineering.com
Signed-off-by: Bjorn Andersson <andersson@kernel.org>