pmdinfogen: fix resource leak of file object

pmdinfogen: fix resource leak of file object

Coverity flags an issue where the resources used by the FILE object for
the temporary input file are leaked. This is a very minor issue, but is
easily fixed, while also avoiding later problems where we try to close
an invalid file descriptor in the failure case.

The fix is to use "dup()" to get a new file descriptor number rather than
using the value directly from fileno. This allows us to close the file
opened with tmpfile() within in scope block, while allowing the duplicate
to pass to the outer block and be closed when the function terminates.

As a side-effect I/O in the function is therefore changed from using stdio
fread/fwrite to read/write system calls.

Coverity issue: 260399
Fixes: 0d68533617e3 ("pmdinfogen: allow using stdin and stdout")

Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>