drm/msm: handle dma_map_attachment before physical address access

The scatter gather table might not be populated while trying
to access the dma_addr of secure-ui/secure-camera buffers.
The physical and dma address are accessible only through the
sg_table. Make sure dma_map_attachment is done before accessing
the dma/phy address.

Change-Id: I3efe953a45fdda155af570d89a92c968c0151d7f
Signed-off-by: Veera Sundaram Sankaran <veeras@codeaurora.org>