i2c: gxp: fix an error code in probe

This is passing IS_ERR() instead of PTR_ERR() so instead of an error
code it prints and returns the number 1.

Fixes: 4a55ed6f

 ("i2c: Add GXP SoC I2C Controller")
Signed-off-by: Dan Carpenter <error27@gmail.com>
Reviewed-by: Nick Hawkins <nick.hawkins@hpe.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>