i2c: s3c2410: fix oops in suspend callback for non-dt platforms

Initialize sysreg by default, otherwise driver will crash in suspend
callback when not using DT.

Signed-off-by: Vasily Khoruzhick <anarsoul@gmail.com>
Reviewed-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Cc: stable@kernel.org
Fixes: a7750c3e ("i2c: s3c2410: Handle i2c sys_cfg register in i2c driver")