PCI: dwc: Fix signedness bug in fault injection test code

PCI: dwc: Fix signedness bug in fault injection test code

The kstrtou32() function returns negative error code or zero on success.
However, in this case "val" is a u32 and the function returns signed long,
so negative error codes from kstrtou32() are returned as high positive
values.

Store the error code in an int instead.

Fixes: d20ee8e2dbd6 ("PCI: dwc: Add debugfs based Error Injection support for DWC")
Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
Reviewed-by: Hans Zhang <18255117159@163.com>
Link: https://patch.msgid.link/agL-Uwfn26SI4Gb0@stanley.mountain