platform: msm_shared: Modify spare bytes calculation in qpic nand

Physical nand device may have more spare bytes than we use. Wrong spare bytes
calculation causes flashing and file system mount issues. So we calculate spare bytes
as the difference of total codeword size and page_size.

CRs-Fixed: 615649
Change-Id: I3c2b3daa95411b786fef2f7eb65636294cf8f925
1 file changed