ext4: check the return value of ext4_xattr_inode_dec_ref()

Check the return value of ext4_xattr_inode_dec_ref(), which could
return error code and need to be warned.

Signed-off-by: Li Zhong <floridsleeves@gmail.com>
Link: https://lore.kernel.org/r/20220917002816.3804400-1-floridsleeves@gmail.com


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