clk: qcom: clk-alpha-pll: Set PLL_UPDATE if configuring the PLL twice

Changes in device versions might lead to the fabia PLL being
configured multiple times. Since the PLL is kept in STANDBY mode
after it's configured for the first time, it is mandatory that
for any new L_VAL updates, the PLL_UPDATE bit be hit. Else, the
PLL will be left running at the previously set frequency.

Change-Id: If6e42675c83332a75dbc18c35b67cec31305dc7a
Signed-off-by: Deepak Katragadda <dkatraga@codeaurora.org>