i2c: altera: use proper variable to hold errno

i2c: altera: use proper variable to hold errno

device_property_read_u32() returns errno or 0, so we should use the
integer variable 'ret' and not the u32 'val' to hold the retval.

Fixes: a239e2640e63 ("i2c: altera: Add Altera I2C Controller driver")
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Thor Thayer <thor.thayer@linux.intel.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>