i2c: s3c2410: make i2c_s3c_irq_nextbyte() void

Fix the following coccicheck warning:

drivers/i2c/busses/i2c-s3c2410.c:391:5-8: Unneeded variable: "ret".
Return "0" on line 552

Signed-off-by: Jason Yan <yanaijie@huawei.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>