efi_loader: fix hii keyboard layout pointer computation

efi_loader: fix hii keyboard layout pointer computation

The EFI_HII_KEYBOARD_LAYOUT field `layout_length' is expressed in bytes,
but we add it to the `layout' pointer with (scaled) pointer arithmetic.
When adding an HII keyboard package with multiple keyboard layouts, this
results in only the first layout being added correctly; fix it.

Fixes: 8d3b77e36e10 ("efi: hii: add keyboard layout package support")
Signed-off-by: Vincent Stehlé <vincent.stehle@arm.com>
Cc: Heinrich Schuchardt <xypron.glpk@gmx.de>
Cc: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Cc: Tom Rini <trini@konsulko.com>
Cc: AKASHI Takahiro <akashi.tkhro@gmail.com>