NTB: perf: Fix an error code in perf_setup_inbuf()

When the function IS_ALIGNED() returns false, the value of ret is 0.
So, we set ret to -EINVAL to indicate this error.

Clean up smatch warning:
drivers/ntb/test/ntb_perf.c:602 perf_setup_inbuf() warn: missing error
code 'ret'.

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Yang Li <yang.lee@linux.alibaba.com>
Reviewed-by: Serge Semin <fancer.lancer@gmail.com>
Signed-off-by: Jon Mason <jdmason@kudzu.us>