mtd: physmap: physmap-bt1-rom: Fix unintentional stack access

Cast &data to (char *) in order to avoid unintentionally accessing
the stack.

Notice that data is of type u32, so any increment to &data
will be in the order of 4-byte chunks, and this piece of code
is actually intended to be a byte offset.

Fixes: b3e79e7682e0 ("mtd: physmap: Add Baikal-T1 physically mapped ROM support")
Addresses-Coverity-ID: 1497765 ("Out-of-bounds access")
Cc: [e-mail]
Signed-off-by: Gustavo A. R. Silva <[e-mail]>
Acked-by: Serge Semin <[e-mail]>
Signed-off-by: Miquel Raynal <[e-mail]>
Link: https://lore.kernel.org/linux-mtd/20210212104022.GA242669@embeddedor

drivers/mtd/maps/physmap-bt1-rom.c

···
 	if (shift) {
 		chunk = min_t(ssize_t, 4 - shift, len);
 		data = readl_relaxed(src - shift);
-		memcpy(to, &data + shift, chunk);
+		memcpy(to, (char *)&data + shift, chunk);
 		src += chunk;
 		to += chunk;
 		len -= chunk;