power: pm8921-bms: handle null scaling factor tables

The scaling factor tables are based on aging of the battery. Sometimes
this data wont be available and these tables will be set to null.

Return 100% scaling factor when scaling factor table is missing.

Change-Id: I730813136d7c9fc10892a29f38449df19b5087a3
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>