x86/ucode/intel: Remove gratuitous memory allocations from cpu_request_microcode()

x86/ucode/intel: Remove gratuitous memory allocations from cpu_request_microcode()

cpu_request_microcode() needs to scan its container and duplicate one blob,
but the get_next_ucode_from_buffer() helper duplicates every blob in turn.
Furthermore, the length checking is only safe from overflow in 64bit builds.

Delete get_next_ucode_from_buffer() and alter the purpose of the saved
variable to simply point somewhere in buf until we're ready to return.

This is only a modest reduction in absolute code size, but avoids making
memory allocations for every blob in the container.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>