msm: clock-mdss: Toggle lock detect before checking for PLL lock

The enable sequences for the DSI PLL for MSM8226 poll a hardware
status register in order to determine whether the PLL has locked.
However, with the current sequences, it is possible that the
hardware status register would indicate a PLL lock even though the
PLL is not really locked. To avoid this, toggle the lock detect
register setting before polling for PLL lock status.

CRs-Fixed: 490476
Change-Id: I6e1357afaa6a86be9ab92095a41768873c70cf0d
Signed-off-by: Aravind Venkateswaran <aravindh@codeaurora.org>