target: correctly handle match_int errors in FILEIO + PSCSI

This patch correctly handles match_int() errors in FILEIO + PSCSI
backend parameter parsing, which can potentially fail due to a
memory allocation failure or invalid argument.

Found by coverity.

Signed-off-by: Joern Engel <joern@logfs.org>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>