haven: Fix non-zero input SG-List handling for MEM_ACCEPT

The MEM_ACCEPT interface assumes that the Resource Manager (RM)
will always return an SG-List. This is not correct when the
caller provides an SG-List, in which case the RM will not return
an SG-List, as it doesn't need to, since the caller knows where
the memory has been mapped. Thus, if the caller specifies an SG-List,
and the MEM_ACCEPT call is successful, then simply return the SG-List
that they provided.

Change-Id: I0ba98adc2f8fc858b1a653da909026a9b626c965
Signed-off-by: Isaac J. Manjarres <isaacm@codeaurora.org>