phy: qcom-ufs-qmp-20nm: fix DIF-Z threshold

In some cases link startup fails due to unexpected
termination caused by DIF-N to DIF-Z transition.
This patch will make PHY look only for DIF-N -> DIF-P
transition and not respond to DIF-N to DIF-Z transition.
Hence prevents a case where DIF-Z is identified as
DIF-P, which may result in unexpected LCC interpretation
and PHY switch to HS.

Change-Id: Ia79fceb245516b96f84d8511e983187e09db254a
Signed-off-by: Maya Erez <merez@codeaurora.org>