s390/protvirt: fix error return code in uv_info_init()

Fix to return a negative error code from the error handling
case instead of 0, as done elsewhere in this function.

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Baisong Zhong <zhongbaisong@huawei.com>
Fixes: 37564ed8 ("s390/uv: add prot virt guest/host indication files")
Link: https://lore.kernel.org/r/2f7d62a4-3e75-b2b4-951b-75ef8ef59d16@huawei.com


Signed-off-by: Heiko Carstens <hca@linux.ibm.com>