Ib/usnic: Explicitly include usnic headers

Sparse tool complains about undeclared symbols in usnic_ib_verbs.c
and usnic_ib_sysfs.c This is caused by lack of direct include of
appropriate usnic_ib_verbs.h and usnic_ib_sysfs.h, where all
these functions were declared.

Simple include eliminates 30 warnings similar to the below one:

drivers/infiniband/hw/usnic/usnic_ib_sysfs.c:304:6: warning: symbol
				'usnic_ib_sysfs_unregister_usdev' was
				not declared. Should it be static?

CC: Christian Benvenuti <benve@cisco.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Doug Ledford <dledford@redhat.com>