i2c: omap: fix usage of IS_ERR_VALUE with pm_runtime_get_sync

we use IS_ERR_VALUE to check for error values of pm_runtime_get_sync,
when the value can only be < 0 in the case of err. Replace the
check with a simpler < 0 check.

This fixes the coccicheck warnings:
linux-2.6/drivers/i2c/busses/i2c-omap.c:1157:5-24:
pm_runtime_get_sync returns < 0 as error. Unecessary IS_ERR_VALUE at
line 1158
linux-2.6/drivers/i2c/busses/i2c-omap.c:1278:7-26:
pm_runtime_get_sync returns < 0 as error. Unecessary IS_ERR_VALUE at
line 1279
drivers/i2c/busses/i2c-omap.c:638:5-24:
pm_runtime_get_sync returns < 0 as error. Unecessary IS_ERR_VALUE at
line 639

Signed-off-by: Nishanth Menon <nm@ti.com>
Reviewed-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>