media: cx25840: don't open-code cx25840_reset() inside cx25840_load_fw()

cx25840_load_fw() does the same thing as cx25840_reset(), only keeps
"is_initialized" flag so any further invocation of this function besides
the first one is a NOP.
Let's just call cx25840_reset() directly from cx25840_load_fw() instead of
open coding it there.

While we are at it, let's also improve comments about cx25840_load_fw()
so they are current and in the proper style (one of them even referred to a
non-existing cx25840 init operation).

Signed-off-by: Maciej S. Szmigiero <mail@maciej.szmigiero.name>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>