i2c: designware-pci: use IRQF_COND_SUSPEND flag

This is effectively reapplies the commit b0898fda ("i2c: designware-pci: use
IRQF_COND_SUSPEND flag") after the commit d80d1341 ("i2c: designware: Move
common probe code into i2c_dw_probe()"). Original message as follows.

The mentioned flag fixes a warning on Intel Edison board since one of the I2C
controller shares IRQ line with watchdog timer.

Fixes: d80d1341 (i2c: designware: Move common probe code into i2c_dw_probe())
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>