mdss: mdp3: verify return value from iommu and bw calls

When driver was enabling/disabling iommu it was not verifying
return values of the call. Same with bw set quota call.

Change-Id: I8755335bffd5d52720f8a5d735427b5306eab512
Signed-off-by: Terence Hampson <thampson@codeaurora.org>