[S390] hypfs: Fix error handling in hypfs_diag initialization

Fix the following two error handling bugs in hypfs_diag_init():
* No need for calling diag204_free_buffer()
* Initialize name table only in case of LPAR and prevent error message
  on non-LPAR systems.

Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>