EDAC, fsl_ddr: Fix IRQ dispose warning when module is removed

When compiled as a module, removing it causes kernel warnings
when irq_dispose_mapping() is called. Instead of calling
irq_of_parse_and_map(), use platform_get_irq() to acquire the IRQ
number.

Signed-off-by: York Sun <york.sun@nxp.com>
Cc: linux-edac <linux-edac@vger.kernel.org>
Cc: morbidrsa@gmail.com
Cc: oss@buserror.net
Cc: stuart.yoder@nxp.com
Link: http://lkml.kernel.org/r/1470779760-16483-8-git-send-email-york.sun@nxp.com


Signed-off-by: Borislav Petkov <bp@suse.de>