ath6kl: Fix the byte alignment rule to avoid loss of bytes in a TCP segment

Either first 3 bytes of the first received tcp segment or last one
over MTU size file can be loss due to the byte alignment problem.
Although ATH6KL_HTC_ALIGN_BYTES was defined for 'extra bytes for htc header
alignment' in the patch "Fix buffer alignment for scatter-gather
I/O"(1df94a857), there exists the bytes loss issue which means that it will be
truncated 3 bytes in the transmitted file contents if a file which has over MTU
size is transferred through TCP/IP stack.  It doesn't look like TCP/IP stack
bug of 3.5 or the latest version of kernel but the byte alignment issue.  This
patch is to use the roundup() function for the byte alignment rather than the
predefined ATH6KL_HTC_ALIGN_BYTES.

kvalo: fixed indentation

Signed-off-by: Myoungje Kim <mjei78@gmail.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>