linux/ctype.h is needed for isalnum() to avoid a build error:
drivers/platform/x86/samsung-laptop.c: In function ‘samsung_sabi_diag’:
drivers/platform/x86/samsung-laptop.c:1306: error: implicit declaration of function ‘isalnum’
Signed-off-by: David Rientjes <rientjes@google.com> Signed-off-by: Corentin Chary <corentincj@iksaif.net> Signed-off-by: Matthew Garrett <mjg@redhat.com>