soc: fsl: qbman: qman: avoid allocating from non existing gen_pool

soc: fsl: qbman: qman: avoid allocating from non existing gen_pool

If the qman driver didn't probe, calling qman_alloc_fqid_range,
qman_alloc_pool_range or qman_alloc_cgrid_range (as done in dpaa_eth) will
pass a NULL pointer to gen_pool_alloc, leading to a NULL pointer
dereference.

Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Reviewed-by: Roy Pledge <roy.pledge@nxp.com>
Signed-off-by: Li Yang <leoyang.li@nxp.com>
(cherry picked from commit f72487a2788aa70c3aee1d0ebd5470de9bac953a)
Signed-off-by: Olof Johansson <olof@lixom.net>