clock: Use .balign to align ticksl

The .align directive has a different behaviour on 32-bit arm than on
other platforms. Use .balign instead, which has consistent behaviour on
all architectures.

Reported by: kib
Reviewed by: jrtc27, kib
Fixes: 6b82130e6c9a ("clock: Add a long ticks variable, ticksl")
Differential Revision: https://reviews.freebsd.org/D48430

(cherry picked from commit 159d29d3948294cdc9ee4cc3951d004de6797a32)