ANDROID: input: keychord: Fix a slab out-of-bounds read.

Fix a slab out of bounds read in keychord_write(), detected by KASAN.

Signed-off-by: Mohan Srinivasan <srmohan@google.com>
Bug: 63962952
Change-Id: Iafef48b5d7283750ac0f39f5aaa767b1c3bf2004

[AmitP: Folded following android-4.9 commit changes into this patch
        a1e4c795e1b6 ("Use %zu to print resid (size_t).")]
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>