fiemap_writer: Fix file pinning / pinning status check code.

The IsFilePinned() function is still not being called because I am still
seeing # blocks moved when I run following test on
aosp_blueline-userdebug.

 $ fiemap_writer_test /dev/block/sda21 \
 --gtest_filter=FiemapWriterTest.CheckWriteError

Bug: 122138114
Test: fiemap_writer_test /dev/block/sda21

Change-Id: I08d74093a082674d621772d202143d2f32e7c665
Signed-off-by: Sandeep Patil <sspatil@google.com>