media: mc: mc-entity.c: Use bitmap_zalloc() when applicable

'ent_enum->bmap' is a bitmap. So use 'bitmap_zalloc()' to simplify
code, improve the semantic and avoid some open-coded arithmetic in
allocator arguments.

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

While at it, remove a useless 'bitmap_zero()'.

Link: https://lore.kernel.org/linux-media/b11f646dda189f490c06bf671f64a2cc0af4d45c.1638397089.git.christophe.jaillet@wanadoo.fr


Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Reviewed-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>