arm64: signal: don't force known signals to SIGKILL

Since commit:

  a7e6f1ca ("arm64: signal: Force SIGKILL for unknown signals in force_signal_inject")

... any signal which is not SIGKILL will be upgraded to a SIGKILL be
force_signal_inject(). This includes signals we do expect, such as
SIGILL triggered by do_undefinstr().

Fix the check to use a logical AND rather than a logical OR, permitting
signals whose layout is SIL_FAULT.

Fixes: a7e6f1ca ("arm64: signal: Force SIGKILL for unknown signals in force_signal_inject")
Cc: Will Deacon <will.deacon@arm.com>
Reviewed-by: Dave Martin <Dave.Martin@arm.com>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/kernel/traps.c

@@ -366,7 +366,7 @@ void force_signal_inject(int signal, int code, unsigned long address)
 	}
 
 	/* Force signals we don't understand to SIGKILL */
-	if (WARN_ON(signal != SIGKILL ||
+	if (WARN_ON(signal != SIGKILL &&
 		    siginfo_layout(signal, code) != SIL_FAULT)) {
 		signal = SIGKILL;
 	}