IB/core: avoid 32-bit warning

The INIT_UDATA() macro requires a pointer or unsigned long argument for
both input and output buffer, and all callers had a cast from when
the code was merged until a recent restructuring, so now we get

core/uverbs_cmd.c: In function 'ib_uverbs_create_cq':
core/uverbs_cmd.c:1481:66: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]

This makes the code behave as before by adding back the cast to
unsigned long.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: 565197dd ("IB/core: Extend ib_uverbs_create_cq")
Reviewed-by: Yann Droneaud <ydroneaud@opteya.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>