ionic: Initialize the 'lif->dbid_inuse' bitmap

When allocated, this bitmap is not initialized. Only the first bit is set a
few lines below.

Use bitmap_zalloc() to make sure that it is cleared before being used.

Fixes: 6461b446

 ("ionic: Add interrupts and doorbells")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Shannon Nelson <snelson@pensando.io>
Link: https://lore.kernel.org/r/6a478eae0b5e6c63774e1f0ddb1a3f8c38fa8ade.1640527506.git.christophe.jaillet@wanadoo.fr


Signed-off-by: Jakub Kicinski <kuba@kernel.org>