I2C: OMAP: correct SYSC register offset for OMAP4

Correct OMAP_I2C_SYSC_REG offset in omap4 register map.
Offset 0x20 is reserved and OMAP_I2C_SYSC_REG has 0x10 as offset.

Signed-off-by: Alexander Aring <a.aring@phytec.de>
[khilman@ti.com: minor changelog edits]
Cc: stable@vger.kernel.org
Signed-off-by: Kevin Hilman <khilman@ti.com>