[COVERITY] Fix missing return code check for ext2fs_write_inode

[COVERITY] Fix missing return code check for ext2fs_write_inode

Found 2 of the three places where a return code for ext2fs_write_inode() was
not being checked.

The second fix in e2fsck/emptydir.c is basically just to shut coverity up even
though it really is unnecessary.

Coverity ID: 1: Checked Return

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>