soc/fsl/qbman: Fix drain_mr_fqni()

The drain_mr_fqni() function may be called fron uninterruptable
context so convert the msleep() to an mdelay().  Also ensure that
the valid bit is updated while polling.

Signed-off-by: Roy Pledge <roy.pledge@nxp.com>
Signed-off-by: Li Yang <leoyang.li@nxp.com>