efi: ARM: avoid warning about phys_addr_t cast

memblock_remove() takes a phys_addr_t, which may be narrower than 64 bits,
causing a harmless warning:

drivers/firmware/efi/arm-init.c: In function 'reserve_regions':
include/linux/kernel.h:29:20: error: large integer implicitly truncated to unsigned type [-Werror=overflow]
 #define ULLONG_MAX (~0ULL)
                    ^
drivers/firmware/efi/arm-init.c:152:21: note: in expansion of macro 'ULLONG_MAX'
  memblock_remove(0, ULLONG_MAX);

This adds an explicit typecast to avoid the warning

Fixes: 500899c2 ("efi: ARM/arm64: ignore DT memory nodes instead of removing them")
Acked-by Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Matt Fleming <matt@codeblueprint.co.uk>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Will Deacon <will.deacon@arm.com>