media: pci: saa7164.c: Replace if(cond) BUG with BUG_ON

Fix the following coccinelle reports:

drivers/media/pci/saa7164/saa7164-buffer.c:254:3-6: WARNING: Use BUG_ON
instead of if condition followed by BUG.

drivers/media/pci/saa7164/saa7164-buffer.c:261:3-6: WARNING: Use BUG_ON
instead of if condition followed by BUG.

Found using - Coccinelle (http://coccinelle.lip6.fr

)

Signed-off-by: Daniel W. S. Almeida <dwlsalmeida@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>