switch do_fsync() to fget_light()

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: franciscofranco <franciscofranco.1990@gmail.com>
Asynchronous Fsync: FIX long bugged fput after commit https://github.com/dorimanx/Dorimanx-LG-G2-D802-Kernel/commit/16b915bbf7f4dbe87fcd019147b30d3c3fd045a3