platform: msm_shared: Fix the OOB error when updating GPT partition

OOB maybe occur when updating GPT partition if the image size is
too small.

1. ebrImage = mbrImage + block_size.
2. primary_gpt_header = (gptImage + block_size).
3. secondary_gpt_header = offset + block_size + primary_gpt_header.

Change-Id: I2a6eccf936b5e9cdc8b705661b1794a41aaafe59
1 file changed