asoc: sdm845: set flag ignore_pmdown_time for ultrasound RX DAI

During PCM closing, the AIF power down will be delayed due to flag
ignore_pmdown_time is not set. Set this flag for ultrasound RX DAI
to avoid delay in PCM close which causes slimbus overflow.

Change-Id: I5eeaceaacc5be0c200b50d1a7d0f211fa0d41f2b
Signed-off-by: Xiaoyu Ye <benyxy@codeaurora.org>