block: m25p80: Fix vmstate structure name

Correct bad name of the vmstate structure. Since this breaks
compatibility also update vmstate version back to 0 and make
all fields independent of the VMState version.

Signed-off-by: Marcin Krzeminski <marcin.krzeminski@nokia.com>
Acked-by: Alistair Francis <alistair.francis@xilinx.com>
Message-id: 1473146346-27337-1-git-send-email-marcin.krzeminski@nokia.com
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>