Camera: Fix possible ExifUtils heap corruption

Both EXIF_TAG_IMAGE_WIDTH and EXIF_TAG_IMAGE_LENGTH
expect short values as per EXIF spec. Call appropriate
libexif function to avoid possible heap corruption.

Bug: 148223871
Test: run sts-engbuild-no-spl-lock -m StsHostTestCases --test android.security.sts.Poc20_02#testPocBug_148223871
Change-Id: I57a774454b52c16d7da9f90d7e3a3407294606a5