mtd: rawnand: docg4: Remove wrong __init annotations

If gcc (e.g. 4.1.2) decides not to inline init_mtd_structs() and
read_id_reg(), this will cause section mismatches, and crashes:

    WARNING: drivers/mtd/nand/raw/docg4.o(.text+0xc10): Section mismatch in reference from the function docg4_attach_chip() to the function .init.text:init_mtd_structs()
    The function docg4_attach_chip() references
    the function __init init_mtd_structs().
    This is often because docg4_attach_chip lacks a __init
    annotation or the annotation of init_mtd_structs is wrong.

    WARNING: drivers/mtd/nand/raw/docg4.o(.text+0xc3e): Section mismatch in reference from the function docg4_attach_chip() to the function .init.text:read_id_reg()
    The function docg4_attach_chip() references
    the function __init read_id_reg().
    This is often because docg4_attach_chip lacks a __init
    annotation or the annotation of read_id_reg is wrong.

Fix this by dropping the now incorrect __init annotations from
init_mtd_structs() and read_id_reg().

Fixes: 66a38478 ("mtd: rawnand: docg4: convert driver to nand_scan()")
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>