sata_fsl: fix warning in remove_proc_entry when rmmod sata_fsl

Trying to remove the fsl-sata module in the PPC64 GNU/Linux
leads to the following warning:
 ------------[ cut here ]------------
 remove_proc_entry: removing non-empty directory 'irq/69',
   leaking at least 'fsl-sata[ff0221000.sata]'
 WARNING: CPU: 3 PID: 1048 at fs/proc/generic.c:722
   .remove_proc_entry+0x20c/0x220
 IRQMASK: 0
 NIP [c00000000033826c] .remove_proc_entry+0x20c/0x220
 LR [c000000000338268] .remove_proc_entry+0x208/0x220
 Call Trace:
  .remove_proc_entry+0x208/0x220 (unreliable)
  .unregister_irq_proc+0x104/0x140
  .free_desc+0x44/0xb0
  .irq_free_descs+0x9c/0xf0
  .irq_dispose_mapping+0x64/0xa0
  .sata_fsl_remove+0x58/0xa0 [sata_fsl]
  .platform_drv_remove+0x40/0x90
  .device_release_driver_internal+0x160/0x2c0
  .driver_detach+0x64/0xd0
  .bus_remove_driver+0x70/0xf0
  .driver_unregister+0x38/0x80
  .platform_driver_unregister+0x14/0x30
  .fsl_sata_driver_exit+0x18/0xa20 [sata_fsl]
 ---[ end trace 0ea876d4076908f5 ]---

The driver creates the mapping by calling irq_of_parse_and_map(),
so it also has to dispose the mapping. But the easy way out is to
simply use platform_get_irq() instead of irq_of_parse_map(). Also
we should adapt return value checking and propagate error values.

In this case the mapping is not managed by the device but by
the of core, so the device has not to dispose the mapping.

Fixes: faf0b2e5

 ("drivers/ata: add support to Freescale 3.0Gbps SATA Controller")
Cc: stable@vger.kernel.org
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Baokun Li <libaokun1@huawei.com>
Reviewed-by: Sergei Shtylyov <sergei.shtylyov@gmail.com>
Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>