fsx: fix leaked log file pointer

fsx: fix leaked log file pointer

Fix a resource leaks in fsx, where we fail to close the fsx logfile,
because the C library could have some buffered contents that aren't
flushed when the program terminates.  glibc seems to do this for us, but
I wouldn't be so sure about the others.

Fixes: 3f742550dfed84 ("fsx: add support for recording operations to a file")
Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Zorro Lang <zlang@kernel.org>