dump_emit(): use __kernel_write(), not vfs_write()

the caller has already done file_start_write()...
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

fs/coredump.c

@@ -695,7 +695,7 @@ int dump_emit(struct coredump_params *cprm, const void *addr, int nr)
 	while (nr) {
 		if (dump_interrupted())
 			return 0;
-		n = vfs_write(file, addr, nr, &pos);
+		n = __kernel_write(file, addr, nr, &pos);
 		if (n <= 0)
 			return 0;
 		file->f_pos = pos;