s390/hypfs: Add missing get_next_ino()

With git commit 85fe4025 ("fs: do not
assign default i_ino in new_inode") the get_next_ino() function was
moved from the new_inode() to the different file system implementations.
Unfortunately hypfs has been overlooked by the author. With this
patch the get_next_ino() is added also to hypfs.

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