drm/udl: Fix unaligned memory access in udl_render_hline

On SPARC, the udl driver filled my kernel log with these messages:

[186668.910612] Kernel unaligned access at TPC[76609c] udl_render_hline+0x13c/0x3a0

Use put_unaligned_be16 to avoid them. On x86 this results in the same
code, but on SPARC the compiler emits two single-byte stores.

Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Acked-by: David Airlie <airlied@linux.ie>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: http://patchwork.freedesktop.org/patch/msgid/20170407200229.20642-1-j.neuschaefer@gmx.net