arm64: __show_regs: strip PAC from lr in printk

lr is printed with %pS which will try to find an entry in kallsyms.
After enabling pointer authentication, this match will fail due to
PAC present in the lr.

Strip PAC from the lr to display the correct symbol name.

Suggested-by: James Morse <james.morse@arm.com>
Signed-off-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Reviewed-by: Vincenzo Frascino <Vincenzo.Frascino@arm.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>