ext4: fix off by one issue in ext4_mb_choose_next_group_best_avail()

In ext4_mb_choose_next_group_best_avail(), we want the start order to be
1 less than goal length and the min_order to be, at max, 1 more than the
original length. This commit fixes an off by one issue that arose due to
the fact that 1 << fls(n) > (n).

After all the processing:

order = 1 order below goal len
min_order = maximum of the three:-
             - order - trim_order
             - 1 order below B2C(s_stripe)
             - 1 order above original len

Cc: stable@kernel.org
Fixes: 33122aa930 ("ext4: Add allocation criteria 1.5 (CR1_5)")
Signed-off-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
Link: https://lore.kernel.org/r/20230609103403.112807-1-ojaswin@linux.ibm.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>