ext4: remove unnecessary fast commit calls from ext4_file_mmap

Remove unnecessary calls to ext4_fc_start_update() and
ext4_fc_stop_update() from ext4_file_mmap().

Signed-off-by: Harshad Shirwadkar <harshadshirwadkar@gmail.com>
Link: https://lore.kernel.org/r/20201106035911.1942128-17-harshadshirwadkar@gmail.com


Signed-off-by: Theodore Ts'o <tytso@mit.edu>