drm/msm: msm_gem_vma.c: fix all kernel-doc warnings

Correct or add kernel-doc comments to eliminate all warnings:

Warning: ../drivers/gpu/drm/msm/msm_gem_vma.c:96 expecting prototype for
struct msm_vma_op. Prototype was for struct msm_vm_op instead

Signed-off-by: Randy Dunlap <[e-mail]>
Reviewed-by: Dmitry Baryshkov <[e-mail]>
Patchwork: https://patchwork.freedesktop.org/patch/695679/
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Dmitry Baryshkov <[e-mail]>

drivers/gpu/drm/msm/msm_gem_vma.c

···
 };
 
 /**
- * struct msm_vma_op - A MAP or UNMAP operation
+ * struct msm_vm_op - A MAP or UNMAP operation
  */
 struct msm_vm_op {
 	/** @op: The operation type */
···
  * synchronous operations are supported.  In a user managed VM, userspace
  * handles virtual address allocation, and both async and sync operations
  * are supported.
+ *
+ * Returns: pointer to the created &struct drm_gpuvm on success
+ * or an ERR_PTR(-errno) on failure.
  */
 struct drm_gpuvm *
 msm_gem_vm_create(struct drm_device *drm, struct msm_mmu *mmu, const char *name,