clk: qcom: clk-cpu-osm: Change logic to enable OSM

On certain targets, there's a WDOG_DEBUG_EN field in the
OSM_ENABLE register that's set by default. This bit is
currently overridden and cleared while enabling OSM from
the clock driver.
Fix the logic to only effect the ENABLE_OSM bit.

Change-Id: I66b182476cc885be5fd9ac91fc030ca5ad2be329
Signed-off-by: Deepak Katragadda <dkatraga@codeaurora.org>