nvmem: u-boot-env: fix crc32_data_offset on redundant u-boot-env

nvmem: u-boot-env: fix crc32_data_offset on redundant u-boot-env

The Western Digital MyBook Live (PowerPC 464/APM82181)
has a set of redundant u-boot-env. Loading up the driver
the following error:

| u_boot_env: Invalid calculated CRC32: 0x4f8f2c86 (expected: 0x98b14514)
| u_boot_env: probe of partition@1e000 failed with error -22

Looking up the userspace libubootenv utilities source [0],
it looks like the "mark" or "flag" is not part of the
crc32 sum... which is unfortunate :(

|static int libuboot_load(struct uboot_ctx *ctx)
|{
|[...]
|       if (ctx->redundant) {
|		[...]
|               offsetdata = offsetof(struct uboot_env_redund, data);
|		[...]					//-----^^
|       }
|       usable_envsize = ctx->size - offsetdata;
|       buf[0] = malloc(bufsize);
|[...]
|	for (i = 0; i < copies; i++) {
|		data = (uint8_t *)(buf[i] + offsetdata);
|               uint32_t crc;
|
|		ret = devread(ctx, i, buf[i]);
|		[...]
|		crc = *(uint32_t *)(buf[i] + offsetcrc);
|               dev->crc = crc32(0, (uint8_t *)data, usable_envsize);
|

[0] https://github.com/sbabic/libubootenv/blob/master/src/uboot_env.c#L951

Fixes: d5542923f200 ("nvmem: add driver handling U-Boot environment variables")
Signed-off-by: Christian Lamparter <chunkeey@gmail.com>
Link: https://lore.kernel.org/r/70a16eae113e08db2390b76e174f4837caa135c3.1667580636.git.chunkeey@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>