md/raid1: remove unnecessary null checking

mainline inclusion
from mainline-next-20231220
commit af140f806ae2679f9dba48ea0f5811da83854eb6
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I8T02O

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=af140f806ae2679f9dba48ea0f5811da83854eb6



--------------------------------

If %__GFP_DIRECT_RECLAIM is set then bio_alloc_bioset will always
be able to allocate a bio. See comment of bio_alloc_bioset.

Signed-off-by: Gou Hao <gouhao@uniontech.com>
Signed-off-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20231214151458.28970-1-gouhao@uniontech.com


Signed-off-by: Li Nan <linan122@huawei.com>