mtd: nand: nandsim: remove unneeded checks for nand_scan_ident/tail()

The nand_scan_ident/tail() never returns a positive value when it
fails.

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>