PCI: xilinx-nwl: Simplify code and fix a memory leak

Allocate space for bitmap in struct nwl_msi at probe time instead of
dynamically allocating the memory at runtime.

This simplifies code (especially error handling paths) and avoid some
open-coded arithmetic in allocator arguments.

This also fixes a potential memory leak. The bitmap was never freed. It
is now part of a managed resource.

Link: https://lore.kernel.org/r/5483f10a44b06aad55728576d489adfa16c3be91.1636279388.git.christophe.jaillet@wanadoo.fr


Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Krzysztof Wilczyński <kw@linux.com>