phy: qcom-ufs-qmp-v3: fix UFS NOP Timeout

With the current SIGDET value of 0x6E there
seems to be NOP timeouts seen frequently.

Hence, change the SIGDET value to 0x6C as per
updated Hardware Programming Guide.

Change-Id: I46426382033603c4727de6b0a485015eed690f34
Signed-off-by: Asutosh Das <asutoshd@codeaurora.org>