Unnecessary conditions in buf_page_get_gen()

Ever since MDEV-10813 cleaned up InnoDB use of atomic memory operations, some conditions around buf_block_fix() have been unnecessary.

Because buf_block_fix() is an atomic operation, there is no need to protect it with an additional mutex, like buf_page_get_gen() did when fsp_is_system_temporary() held.

UNIV_INLINE

ulint

buf_block_fix(

	buf_page_t*	bpage)

{

	return(my_atomic_add32((int32*) &bpage->buf_fix_count, 1) + 1);

}

We shall remove the unnecessary bloat in buf_page_get_gen(). It might slightly improve performance in any operations that access the InnoDB buffer pool, and improve performance a little more on InnoDB temporary tables.