s390/uv: fix memblock virtual vs physical address confusion

memblock_alloc_try_nid() returns a virtual address, however in error
case the allocated memory is incorrectly freed with memblock_phys_free().
Properly use memblock_free() instead, and pass a physical address to
uv_init() to fix this.

Note: this doesn't fix a bug currently, since virtual and physical
addresses are identical.

Reviewed-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>