The current logic, regardless of whether CONFIG_BLK_DEV_ZONED
is enabled or not, will judge whether discard_unit is SECTION,
when f2fs_sb_has_blkzoned.
In fact, when CONFIG_BLK_DEV_ZONED is not enabled, this judgment
is a path that will never be accessed. At this time, -EINVAL will
be returned in the parse_options function, accompanied by the
message "Zoned block device support is not enabled".
Let's wrap this discard_unit judgment with CONFIG_BLK_DEV_ZONED.
Signed-off-by: Yangtao Li <frank.li@xxxxxxxx>