IB/ehca: Catch failing ioremap()

When ioremap() fails with a NULL pointer, catch the error and pass it
to the caller of create_qp() or create_cq() instead of trying to
dereference the NULL pointer later on.

Signed-off-by: Alexander Schmidt <alexs@linux.vnet.ibm.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>