package/qdecoder: Fix build error

Error occured with an allyespackageconfig setup, with
BR2_ENABLE_DEBUG=y:

qcgireq.c: In function '_parse_multipart_value_into_disk':
qcgireq.c:738:60: error: 'errno' undeclared (first use in this function)
         DEBUG("I/O error. (errno=%d)", (ioerror == true) ? errno : 0);

Also fixes the same issue, seen by the autobuilders:

  http://autobuild.buildroot.org/results/ec0/ec06b196e0fe1e2cccb660c683cd1ba012c7f8c7/



[Thomas: add reference to autobuilder failure.]

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>