msm: camera: Avoid writing wrong reg in BF_scale stats configuration

BUS_STATS_BF_SCALE_XXXX unlike other STATS, only contains PING, PONG and
UB_CFG (not FRAMEDROP_PATTERN, ADDR_CFG and IRQ_SUBSAMPLE_PATTERN).
But the current code assumes they are present and configure such
registers, overwriting other registers. Fix added to avoid writing
those registers for configuring BF Scale stats.

Change-Id: Idb1b8ec32b456484ae39996c7fde595ab055a340
Signed-off-by: Sagar Gore <sgore@codeaurora.org>