pppd/crypto: fix gcc 14 build #631

Job	Run time
Buildroot (qemu_x86_defconfig, glibc)	2m 30s
Buildroot (qemu_x86_defconfig, uclibc)	2m 16s
Buildroot (qemu_x86_defconfig, musl)	1m 30s
Buildroot (qemu_x86_64_defconfig, glibc)	1m 45s
Buildroot (qemu_x86_64_defconfig, uclibc)	1m 46s
Buildroot (qemu_x86_64_defconfig, musl)	1m 37s
Buildroot (raspberrypi4_defconfig, glibc)	2m 24s
Buildroot (raspberrypi4_defconfig, uclibc)	1m 49s
Buildroot (raspberrypi4_defconfig, musl)	1m 50s
Buildroot (raspberrypi4_64_defconfig, glibc)	2m 23s
Buildroot (raspberrypi4_64_defconfig, uclibc)	1m 49s
Buildroot (raspberrypi4_64_defconfig, musl)	2m 20s
Buildroot (qemu_ppc64le_pseries_defconfig, glibc)	2m 24s
Buildroot (qemu_ppc64le_pseries_defconfig, uclibc)	1m 45s
Buildroot (qemu_ppc64le_pseries_defconfig, musl)	1m 36s
Buildroot (qemu_mips32r2_malta_defconfig, glibc)	1m 38s
Buildroot (qemu_mips32r2_malta_defconfig, uclibc)	2m 14s
Buildroot (qemu_mips32r2_malta_defconfig, musl)	2m 13s
Buildroot (qemu_mips64_malta_defconfig, glibc)	2m 21s
Buildroot (qemu_mips64_malta_defconfig, uclibc)	1m 36s
Buildroot (qemu_mips64_malta_defconfig, musl)	1m 45s
Buildroot (qemu_riscv32_virt_defconfig, glibc)	2m 19s
Buildroot (qemu_riscv32_virt_defconfig, uclibc)	1m 38s
Buildroot (qemu_riscv32_virt_defconfig, musl)	1m 40s
Buildroot (qemu_riscv64_virt_defconfig, glibc)	1m 40s
Buildroot (qemu_riscv64_virt_defconfig, uclibc)	2m 16s
Buildroot (qemu_riscv64_virt_defconfig, musl)	2m 14s
	53m 18s

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