ib_core: initialize shpd field when allocating 'struct ib_pd'

ib_core: initialize shpd field when allocating 'struct ib_pd'

The shared pd feature in Oracle Linux was added by
commit a1911c2c180d ("IB/Shared PD support from Oracle").
It adds a field named shpd to 'struct ib_pd' but fails to
initialize it in all the places it is allocated.

This results its uninitialized content being referenced
in mlx4_ib_dealloc_pd() and actions taken based on it
which eventually leads to resource leaks even when shared
pd feature is not being used.

This fix here initializes it to NULL in ib_alloc_pd() where
the ib_core module allocates the data structure.

Orabug: 29384815

Signed-off-by: Mukesh Kacker <mukesh.kacker@oracle.com>
Reviewed-by: Rama Nichanamatlu <rama.nichanamatlu@oracle.com>
Reviewed-by: Håkon Bugge <haakon.bugge@oracle.com>
Signed-off-by: Brian Maly <brian.maly@oracle.com>