disp: msm: sde: avoid double mmu destroy during mmu init failure

mmu destroy is called in _sde_kms_mmu_destroy as part of
smmu_aspace_destroy. This change avoids msm_smmu already getting
freed at smmu_aspace_destroy.

Change-Id: I00ff2a99295534189ceec7c769cd0a01762408c2
Signed-off-by: Raviteja Tamatam <travitej@codeaurora.org>