[media] mantis_pci: remove asm/pgtable.h include

mantis_pci.c is including asm/pgtable.h and it's leading to a build failure on
arm. It has been noticed here :

https://buildd.debian.org/fetch.cgi?pkg=linux-2.6&arch=armel&ver=2.6.38~rc6-1~experimental.1&stamp=1298430952&file=log&as=raw

As this header doesn't seem to be used, I'm removing it. I've build tested it
with arm and x86.

Signed-off-by: Arnaud Patard <arnaud.patard@rtp-net.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>