qemuBuildSCSIiSCSIHostdevDrvStr: Don't leak @netsource and @srcprops

After 6b770f9a both @netsource and @srcprops are leaked
because of early return introduced in the commit.

==1812== 644 bytes in 4 blocks are definitely lost in loss record 835 of 885
==1812==    at 0x4C2F12F: realloc (vg_replace_malloc.c:785)
==1812==    by 0x8846393: xmlSaveUriRealloc (in /usr/lib64/libxml2.so.2.9.8)
==1812==    by 0x8846B1C: xmlSaveUri (in /usr/lib64/libxml2.so.2.9.8)
==1812==    by 0x5DDA619: virURIFormat (viruri.c:256)
==1812==    by 0x56E941B: qemuBuildNetworkDriveURI (qemu_command.c:781)
==1812==    by 0x56E979A: qemuBuildNetworkDriveStr (qemu_command.c:859)
==1812==    by 0x56F3A0B: qemuBuildSCSIiSCSIHostdevDrvStr (qemu_command.c:4664)
==1812==    by 0x56F3D1F: qemuBuildSCSIHostdevDrvStr (qemu_command.c:4732)
==1812==    by 0x56F57F7: qemuBuildHostdevCommandLine (qemu_command.c:5337)
==1812==    by 0x570303A: qemuBuildCommandLine (qemu_command.c:10376)
==1812==    by 0x57604EE: qemuProcessCreatePretendCmd (qemu_process.c:6649)
==1812==    by 0x11352A: testCompareXMLToArgv (qemuxml2argvtest.c:566)
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>

src/qemu/qemu_command.c

@@ -4644,8 +4644,8 @@ static char *
 qemuBuildSCSIiSCSIHostdevDrvStr(virDomainHostdevDefPtr dev,
                                 virQEMUCapsPtr qemuCaps)
 {
+    char *ret = NULL;
     virBuffer buf = VIR_BUFFER_INITIALIZER;
-
     char *netsource = NULL;
     virJSONValuePtr srcprops = NULL;
     virDomainHostdevSubsysSCSIPtr scsisrc = &dev->source.subsys.u.scsi;
@@ -4672,13 +4672,13 @@ qemuBuildSCSIiSCSIHostdevDrvStr(virDomainHostdevDefPtr dev,
     if (virBufferCheckError(&buf) < 0)
         goto cleanup;
 
-    return virBufferContentAndReset(&buf);
+    ret = virBufferContentAndReset(&buf);
 
  cleanup:
     VIR_FREE(netsource);
     virJSONValueFree(srcprops);
     virBufferFreeAndReset(&buf);
-    return NULL;
+    return ret;
 }
 
 char *