video: uvesafb: Remove redundant NULL check

kfree on a NULL pointer is a no-op.

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Cc: Michal Januszewski <spock@gentoo.org>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>