Staging: ipack/carriers: fix missing include linux/slab.h

Kernel build failed for parisc architecture:

drivers/staging/ipack/carriers/tpci200.c: In function 'tpci200_free_irq':
drivers/staging/ipack/carriers/tpci200.c:190:2: error: implicit declaration of
function 'kfree' [-Werror=implicit-function-declaration]
drivers/staging/ipack/carriers/tpci200.c: In function 'tpci200_request_irq':
drivers/staging/ipack/carriers/tpci200.c:217:2: error: implicit declaration of
function 'kzalloc' [-Werror=implicit-function-declaration]

Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Samuel Iglesias Gonsalvez <siglesias@igalia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>