The mpage bio alloc cleanup accidentally removed clearing ~GFP_KERNEL
bits from the mask passed to bio_alloc.  Fix this up in a slightly
less obsfucated way that mirrors what iomap does in its readpage code.

Fixes: 77c436de ("mpage: pass the operation to bio_alloc")
Reported-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Tested-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Link: https://lore.kernel.org/r/20220323153952.1418560-1-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>