net/smc: Fix ENODATA tests in smc_nl_get_fback_stats()

mainline inclusion
from mainline-v5.14-rc1
commit 1a1100d5
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I78IFM
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit?id=1a1100d53f12451d50bc5ebbc941517760912ab8



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

These functions return negative ENODATA but the minus sign was left out
in the tests.

Fixes: f0dd7bf5 ("net/smc: Add netlink support for SMC fallback statistics")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Guvenc Gulce <guvenc@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>