init.rc: set f2fs seq_file_ra_mul to 128

Based on experiments, we fount out 128 (128 x global readahead window
size = 16mb) is the optimal multiple to boost up read speeds for the
sequentially accessed files with POSIX_FADV_SEQUENTIAL.

Bug: 195311558
Test: check the /sys/fs/f2fs/<userdata partition>/seq_file_ra_mul value
Change-Id: I7563ad6e47b9ab76ae7fe36978d0e5970a7490e8
Signed-off-by: Daeho Jeong <daehojeong@google.com>