efi: x86: Fix config name for setting the NX-compatibility flag in the PE header

efi: x86: Fix config name for setting the NX-compatibility flag in the PE header

Commit 21b68da7bf4a ("efi: x86: Set the NX-compatibility flag in the PE
header") intends to set the compatibility flag, i.e.,
IMAGE_DLL_CHARACTERISTICS_NX_COMPAT, but this ifdef is actually dead as
the CONFIG_DXE_MEM_ATTRIBUTES Kconfig option does not exist.

The config is actually called EFI_DXE_MEM_ATTRIBUTES. Adjust the ifdef
to use the intended config name.

The issue was identified with ./scripts/checkkconfigsymbols.py.

Fixes: 21b68da7bf4a ("efi: x86: Set the NX-compatibility flag in the PE header")
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Link: https://lore.kernel.org/r/20220601115043.7678-1-lukas.bulwahn@gmail.com
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>