sparc64: mdesc: use __GFP_REPEAT action modifier for VM allocation

During MDESC handle allocation, use the __GFP_REPEAT flag instead of
__GFP_NOFAIL. If memory is not available, the caller expects a NULL
pointer instead of waiting until memory is allocated.

Signed-off-by: Jagannathan Raman <jag.raman@oracle.com>
Reviewed-by: Liam Merwick <liam.merwick@oracle.com>
Reviewed-by: Shannon Nelson <shannon.nelson@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>