staging: spectra needs <linux/slab.h>

On one of my m68k test builds I get:

drivers/staging/spectra/ffsport.c: In function ‘ioctl_read_page_data’:
drivers/staging/spectra/ffsport.c:196: error: implicit declaration of function ‘kmalloc’
drivers/staging/spectra/ffsport.c:196: warning: assignment makes pointer from integer without a cast
drivers/staging/spectra/ffsport.c:212: error: implicit declaration of function ‘kfree’
drivers/staging/spectra/ffsport.c: In function ‘ioctl_write_page_data’:
drivers/staging/spectra/ffsport.c:229: warning: assignment makes pointer from integer without a cast
drivers/staging/spectra/ffsport.c: In function ‘SBD_setup_device’:
drivers/staging/spectra/ffsport.c:637: warning: assignment makes pointer from integer without a cast

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Pekka Enberg <penberg@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>