Follow-up to MDEV-13103: Do not add __attribute__((nonnull))

In XtraDB, buf_block_get_frame() can return NULL, and this value
can be passed to buf_page_print(). Do not declare the parameter
as nonnull.

storage/xtradb/include/buf0buf.h

@@ -725,7 +725,7 @@ buf_print(void);
 UNIV_INTERN
 void
 buf_page_print(const byte* read_buf, ulint zip_size)
-	UNIV_COLD MY_ATTRIBUTE((nonnull));
+	UNIV_COLD;
 
 /********************************************************************//**
 Decompress a block.