bcachefs: rename version -> bversion for big endian builds

Builds on big endian systems fail as follows.

fs/bcachefs/bkey.h: In function 'bch2_bkey_format_add_key':
fs/bcachefs/bkey.h:557:41: error:
'const struct bkey' has no member named 'bversion'

The original commit only renamed the variable for little endian builds.
Rename it for big endian builds as well to fix the problem.

Fixes: cf49f8a8c277 ("bcachefs: rename version -> bversion")
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>