mtd: nand: denali: return error code from devm_request_irq() on error

The devm_request_irq() returns an appropriate error value when it
fails.  Use it instead of the fixed -ENODEV.

While we are here, reword the comment to make it fit in a single
line, fixing the misspelling of "initialization".

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Marek Vasut <marek.vasut@gmail.com>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>