soundwire: qcom: remove unused rd_fifo_depth

soundwire: qcom: remove unused rd_fifo_depth

remove read fifo depth field parsing logic, as rd_fifo_depth is never
used in the driver. Cleaning this up would benefit when adding new
variant support which includes adding variant fields for rd_fifo_depth.

ex: Glymur has this rd_fifo_depth register fields changed from v2.x

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@oss.qualcomm.com>
Reviewed-by: Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>
Tested-by: Alexey Klimov <alexey.klimov@linaro.org> # sm8550
Link: https://patch.msgid.link/20250912083225.228778-3-srinivas.kandagatla@oss.qualcomm.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>