media: dvb: Change separated-PES header pipe descriptor size

Setting the header pipe descriptor size to be the same exact size as
the data written by TSPP2 for each PES causes a race-condition between
TSPP2 setting the EOT flag, and BAM driver interrupt handler collecting
the complete descriptor since it is now full.
In addition, descriptor needs to be able to contain two headers in case
PES header spreads over more than a single TS packet.

Change-Id: Iad835e62505330721070a81bb2768fedfb26ca87
Signed-off-by: Gilad Broner <gbroner@codeaurora.org>