carl9170: Use the bitmap API when applicable

Use 'bitmap_zalloc()' to simplify code, improve the semantic and avoid some
open-coded arithmetic in allocator arguments.

Note, that this 'bitmap_zalloc()' divides by BITS_PER_LONG the amount of
memory allocated.
The 'roundup()' used to computed the number of needed long should have
been a DIV_ROUND_UP.


Also change the corresponding 'kfree()' into 'bitmap_free()' to keep
consistency.

Use 'bitmap_zero()' to avoid hand writing it.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Acked-by: Christian Lamparter <chunkeey@gmail.com>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/1fe18fb73f71d855043c40c83865ad539f326478.1638396221.git.christophe.jaillet@wanadoo.fr