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

In the Linux kernel, the following vulnerability has been resolved: 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. Addresses-Coverity-ID: 1497765 ("Out-of-bounds access")