As platform_driver_register() could fail, it should be better
to deal with the return value in order to maintain the code
consisitency.

Fixes: 56a1485b ("i2c: npcm7xx: Add Nuvoton NPCM I2C controller driver")
Signed-off-by: Jiasheng Jiang <jiasheng@iscas.ac.cn>
Acked-by: Tali Perry <tali.perry1@gmail.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>