i2c: xgene-slimpro: Fix wrong pointer passed to PTR_ERR()

mainline inclusion
from mainline-v5.16-rc1
commit c80be257
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I6Z91B
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?h=v6.3-rc2&id=c80be257a4cd0f72c083e6056ff0ce2da871e9dc



--------------------------------

PTR_ERR should access the value just tested by IS_ERR, otherwise
the wrong error code will be returned.

Fixes: 7b6da7fe ("mailbox: pcc: Use PCC mailbox channel pointer instead of standard")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Reviewed-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>