firmware: zynqmp: Handle errors from ipi_req properly

There are multiple errors what can happen in ipi_req but they are not
propagated properly. That's why propage all error properly.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Reviewed-by: Adrian Fiergolski <Adrian.Fiergolski@fastree3d.com>
Link: https://lore.kernel.org/r/7ac4f3b2104f04c72d287c46d1ccbce20f138fd4.1634309856.git.michal.simek@xilinx.com