If kmemdup fails, We need kfree *buff* first then return -ENOMEM.
Otherwise there is a memory leak.
Signed-off-by: NPan Xinhui <xinhui.pan@linux.vnet.ibm.com>
Reviewed-by: NNathan Fontenot <nfont@linux.vnet.ibm.com>
Signed-off-by: NMichael Ellerman <mpe@ellerman.id.au>