err.3: Fix an example

[0mp]

Summary

err.3: Fix an example

The example says that it shows the use of warn*() functions. Replace the err() function there with a warn() call.

Reported by:	yuripv

[jilles]

lib/libc/gen/err.3

199

This doesn't compile, since warn() doesn't take an int eval.

In general, the example seems OK as is, since the warnx() above gives a warning only, and opening some sort of device is apparently required.

The duality of raw and block devices no longer exists, so the example is a bit out of date.

Although warnings like these can be useful, they cannot be used in most POSIX-specified utilities used in the way specified by the standard. POSIX indicates this with the text "The standard error shall be used only for diagnostic messages." A "diagnostic message" implies that the exit status is not 0.