gdma_obj_handle_t is no more than redefinition of basic
u64 type. Remove such obfuscation.

Link: https://lore.kernel.org/r/3c1e821279e6a165d058655d2343722d6650e776.1668160486.git.leonro@nvidia.comAcked-by: Long Li <longli@microsoft.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>