[ACPI] fix kmalloc size bug in acpi/video.c

acpi_video_device_find_cap() used &p instead of *p
when calculating storage size, thus allocating
only 4 or 8 bytes instead of 12...

Also, kfree(NULL) is legal, so remove some unneeded checks.

From: Paulo Marques <pmarques@grupopie.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Len Brown <len.brown@intel.com>