mfd: tps6586x: Fix cast to restricted __le32 warning

Silences Sparse warning(s):

 drivers/mfd/tps6586x.c:323:16: warning: cast to restricted __le32
 drivers/mfd/tps6586x.c:323:16: warning: cast to restricted __le32
 drivers/mfd/tps6586x.c:323:16: warning: cast to restricted __le32
 drivers/mfd/tps6586x.c:323:16: warning: cast to restricted __le32
 drivers/mfd/tps6586x.c:323:16: warning: cast to restricted __le32
 drivers/mfd/tps6586x.c:323:16: warning: cast to restricted __le32

Cc: Mike Rapoport <mike@compulab.co.il>
Cc: Eric Miao <eric.miao@marvell.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>