As the possible failure of the ioremap(), the par_io could be NULL.
Therefore it should be better to check it and return error in order to
guarantee the success of the initiation.
But, I also notice that all the caller like mpc85xx_qe_par_io_init() in
`arch/powerpc/platforms/85xx/common.c` don't check the return value of
the par_io_init().
Actually, par_io_init() needs to check to handle the potential error.
I will submit another patch to fix that.
Anyway, par_io_init() itsely should be fixed.

Fixes: 7aa1aa6e ("QE: Move QE from arch/powerpc to drivers/soc")
Signed-off-by: Jiasheng Jiang <jiasheng@iscas.ac.cn>
Signed-off-by: Li Yang <leoyang.li@nxp.com>