ext4: remove redundant variable has_bigalloc in ext4_fill_super

We can use the ext4_has_feature_bigalloc() function directly to check
bigalloc feature and the variable has_bigalloc is reduncant, so remove
it.

Signed-off-by: Kaixu Xia <kaixuxia@tencent.com>
Reviewed-by: Andreas Dilger <adilger@dilger.ca>
Link: https://lore.kernel.org/r/1586935542-29588-1-git-send-email-kaixuxia@tencent.com


Signed-off-by: Theodore Ts'o <tytso@mit.edu>