gen_init_cpio: fixed fwrite warning

On compilers with security warnings enabled by default, we get:

usr/gen_init_cpio.c: In function ‘cpio_mkfile’:
usr/gen_init_cpio.c:357: warning: ignoring return value of ‘fwrite’,
                                  declared with attribute warn_unused_result

So check the return value and handle errors accordingly.
Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Michal Marek <mmarek@suse.cz>

usr/gen_init_cpio.c

@@ -354,7 +354,10 @@ static int cpio_mkfile(const char *name, const char *location,
 		push_pad();
 
 		if (size) {
-			fwrite(filebuf, size, 1, stdout);
+			if (fwrite(filebuf, size, 1, stdout) != 1) {
+				fprintf(stderr, "writing filebuf failed\n");
+				goto error;
+			}
 			offset += size;
 			push_pad();
 		}