i2c: omap: fix cleanup regression

Patch "i2c: omap: abolish variable name confusion" triggered a
coccinelle warning which we fix here:

drivers/i2c/busses/i2c-omap.c:1333:5-24: pm_runtime_get_sync returns < 0 as error. Unecessary IS_ERR_VALUE at line 1334

Signed-off-by: Wolfram Sang <wsa@the-dreams.de>