saa7134: Fix bytesperline not being set correctly for planar formats

commit 3e71da19f9dc22e39a755d6ae9678661abb66adc upstream.

bytesperline should be the bytesperline for the first plane for planar
formats, not that of all planes combined.

This fixes a crash in xawtv caused by the wrong bpl.

BugLink: https://bugzilla.redhat.com/show_bug.cgi?id=1305389
Reported-and-tested-by: Stas Sergeev <stsp@list.ru>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
[bwh: Backported to 3.2: adjust filename, context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>