i2c: mlxbf: Fix resrticted cast warning of sparse

Address warnings "warning: cast to restricted __be32" reported
by sparse.

Fixes: b5b5b320 ("i2c: mlxbf: I2C SMBus driver for Mellanox BlueField SoC")
Reported-by: kernel test robot <lkp@intel.com>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Reviewed-by: Vadim Pasternak <vadimp@nvidia.com>
Signed-off-by: Khalil Blaiech <kblaiech@nvidia.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>