IB/ehca: fix maybe-uninitialized warnings

The driver causes two warnings about possibly uninitialized variables:

drivers/infiniband/hw/ehca/ehca_mrmw.c: In function 'ehca_set_pagebuf':
drivers/infiniband/hw/ehca/ehca_mrmw.c:1908:4: warning: 'prev_pgaddr' may be used uninitialized in this function [-Wmaybe-uninitialized]
drivers/infiniband/hw/ehca/ehca_mrmw.c:1924:14: note: 'prev_pgaddr' was declared here
drivers/infiniband/hw/ehca/ehca_mrmw.c: In function 'ehca_reg_mr':
drivers/infiniband/hw/ehca/ehca_mrmw.c:2430:5: warning: 'hret' may be used uninitialized in this function [-Wmaybe-uninitialized]

The first one is definitely a false positive, the second one may or may not
be one. In both cases, adding an intialization is the safe and easy
workaround.

The driver was removed in mainline in commit e581d111
("staging/rdma: remove deprecated ehca driver"), in linux-4.6.
In 4.4, the file is located in drivers/staging/rdma/ehca/ehca_mrmw.c,
and the fix still applies.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>