msm: wfd: Add error handling for input buffer ion map failure

Target reset happens when trying to do a ion_unmap_iommu
on the above fd, which was never mapped. Added a check for
non-zero virtual address.

Change-Id: I663cf20b68978d23cf91c7257cd2a5cc9f0ba7e6
CRs-Fixed: 394779
Signed-off-by: Srinu Gorle <sgorle@codeaurora.org>