i2c: sun6i-p2wi: use proper return value in probe

Fixes:
>> drivers/i2c/busses/i2c-sun6i-p2wi.c:243:10: warning: 'ret' may be used uninitialized in this function [-Wmaybe-uninitialized]

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>