i2c: npcm: Correct register access width

The SMBnCTL3 register is 8-bit wide and the 32-bit access was always
incorrect, but simply didn't cause a visible error on the 32-bit machine.

On the 64-bit machine, the kernel message reports that ESR value is
0x96000021. Checking Arm Architecture Reference Manual Armv8 suggests that
it's the alignment fault.

SMBnCTL3's address is 0xE.

Fixes: 56a1485b ("i2c: npcm7xx: Add Nuvoton NPCM I2C controller driver")
Signed-off-by: Tyrone Ting <kfting@nuvoton.com>
Reviewed-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Signed-off-by: Wolfram Sang <wsa@kernel.org>