staging/easycap: PAGE_SIZE is always defined

I'm not 100% sure, only 99.99% that PAGE_SIZE is always defined in
Linux. So there is no need to check for it.

Cc: Mike Thomas <rmthomas@sciolus.org>
Signed-off-by: Kirill Smelkov <kirr@mns.spb.ru>
Acked-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>