out_file: use flb_errno() instead to print message
out_file: use flb_errno() instead to print message

Modified according to the following discussion;
https://groups.google.com/forum/#!topic/fluent-bit/dOWf61ggRXo

Signed-off-by: takahasi <33bdcc34846fccbaac0eed5c29bacf7e1684967a@gmail.com>

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