riscv: make patch-function pointer more generic in cpu_manufacturer_info struct

During review the naming of the function-pointer was called
confusing as the vendor id is just one of three inputs for
the patching and indeed it serves no real purpose, as with
recent changes the function pointer is not a static
global element anymore, so drop the "vendor_" prefix.

Suggested-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://lore.kernel.org/r/20220526205646.258337-4-heiko@sntech.de
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>