tune2fs: abort when trying to enable/disable metadata_csum on mounted fs

Earlier, I tried to make tune2fs abort if the user tried to enable or
disable metadata_csum on a mounted FS, but forgot the exit() call.
Supply it now.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
1 file changed