ARM: mvebu: drop unnecessary label

The label mvebu_boot_wa_start is not necessary and causes a build
issue when building with LLVM's integrated assembler:
    AS      arch/arm/mach-mvebu/pmsu_ll.o
  arch/arm/mach-mvebu/pmsu_ll.S:59:1: error: invalid symbol redefinition
  mvebu_boot_wa_start:
  ^

Drop the label.

Signed-off-by: Stefan Agner <stefan@agner.ch>
Acked-by: Nicolas Pitre <nico@fluxnic.net>
Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>