msm: ADSPRPC: Remove scatterlist validation

The buffers allocated by ION for ADSP/AUDIO heap would be
physically contiguous and no additional checks are required
to validate this.

Change-Id: Ib54aaf6c18448d18d0a22dac0ddab50a0ab4f493
Acked-by: Sathish Ambley <sambley@qti.qualcomm.com>
Signed-off-by: Mitchel Humpherys <mitchelh@codeaurora.org>