staging: i4l: pcbit: replace some include asm/*.h with linux/*.h

Fixes the following checkpatch output:

./pcbit/capi.c:39: WARNING: Use #include <linux/io.h> instead of <asm/io.h>
./pcbit/capi.c:40: WARNING: Use #include <linux/string.h> instead of <asm/string.h>
./pcbit/callbacks.c:25: WARNING: Use #include <linux/io.h> instead of <asm/io.h>
./pcbit/layer2.c:39: WARNING: Use #include <linux/io.h> instead of <asm/io.h>
./pcbit/drv.c:34: WARNING: Use #include <linux/string.h> instead of <asm/string.h>
./pcbit/drv.c:35: WARNING: Use #include <linux/io.h> instead of <asm/io.h>
./pcbit/edss1.c:26: WARNING: Use #include <linux/io.h> instead of <asm/io.h>

Signed-off-by: Alexander Alemayhu <alexander@alemayhu.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>