tx4939ide: typo fix and minor cleanup

The bcount is greater than 0 and less than or equal to 0x10000.
Thus '(bcount & 0xffff) == 0x0000' can be simplified as 'bcount == 0x10000'.

Suggested-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>