savevm.c: fix warning with _FORTIFY_SOURCE

CC    savevm.o
cc1: warnings being treated as errors
savevm.c: In function 'file_put_buffer':
savevm.c:342: error: ignoring return value of 'fwrite', declared with attribute warn_unused_result
make: *** [savevm.o] Error 1

Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>

savevm.c

@@ -339,8 +339,7 @@ static int file_put_buffer(void *opaque, const uint8_t *buf,
 {
     QEMUFileStdio *s = opaque;
     fseek(s->stdio_file, pos, SEEK_SET);
-    fwrite(buf, 1, size, s->stdio_file);
-    return size;
+    return fwrite(buf, 1, size, s->stdio_file);
 }
 
 static int file_get_buffer(void *opaque, uint8_t *buf, int64_t pos, int size)