Fix f2fs_trim_device multiple definitions
Fix f2fs_trim_device multiple definitions

The host tool (make_f2fs) will override the f2fs_trim_device function.
Add weak attribute to the f2fs_trim_device function in f2fs_format_utils.c
Otherwise multiple definitions of symbols will occurs.

Change-Id: Icfb1557e0b9b0bf5102845193d6ab0ef2a9c0bae

TeamTwisted/android_external_f2fs-tools,TeamTwisted/android_external_f2fs-tools