buffer: remove __getblk_gfp()

Inline it into __bread_gfp().

Link: https://lkml.kernel.org/r/20230914150011.843330-9-willy@infradead.org


Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Hui Zhu <teawater@antgroup.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>