Fix bogus error message from merge-recursive error path

Fix bogus error message from merge-recursive error path

This error message should not usually trigger, but the function
make_cache_entry() called by add_cacheinfo() can return early
without calling into refresh_cache_entry() that sets cache_errno.

Also the error message had a wrong function name reported, and
it did not say anything about which path failed either.

Signed-off-by: Junio C Hamano <redacted>