scripts/mksysmap: Fix escape chars '$'

Commit b18b0470 ("kbuild: change scripts/mksysmap into sed script")
changed the invocation of the script, to call sed directly without
shell.

That means, the current extra escape that was added in:
commit ec336aa8 ("scripts/mksysmap: Fix badly escaped '$'")
for the shell is not correct any more, at the moment the stack traces
for nvhe are corrupted:
[   22.840904] kvm [190]:  [<ffff80008116dd54>] __kvm_nvhe_$x.220+0x58/0x9c
[   22.842913] kvm [190]:  [<ffff8000811709bc>] __kvm_nvhe_$x.9+0x44/0x50
[   22.844112] kvm [190]:  [<ffff80008116f8fc>] __kvm_nvhe___skip_pauth_save+0x4/0x4

With this patch:
[   25.793513] kvm [192]: nVHE call trace:
[   25.794141] kvm [192]:  [<ffff80008116dd54>] __kvm_nvhe_hyp_panic+0xb0/0xf4
[   25.796590] kvm [192]:  [<ffff8000811709bc>] __kvm_nvhe_handle_trap+0xe4/0x188
[   25.797553] kvm [192]:  [<ffff80008116f8fc>] __kvm_nvhe___skip_pauth_save+0x4/0x4

Fixes: b18b0470 ("kbuild: change scripts/mksysmap into sed script")
Signed-off-by: Mostafa Saleh <smostafa@google.com>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>