riscv: don't warn for sifive erratas in modules

The SiFive errata code contains code checking applicable erratas
vs. actually applied erratas to suggest missing erratas to the
user when their Kconfig options are not enabled.

In the main kernel image one can be quite sure that all available
erratas appear at least once, so that check will succeed.
On the other hand modules can very well not use any errata-relevant
code, so the newly added module-alternative support may also patch
the module code, but not touch SiFive-specific erratas at all.

So to restore the original behaviour don't warn when patching
modules. This will keep the warning if necessary for the main kernel
image but prevent spurious warnings for modules.

Of course having such a vendor-specific warning may not be needed at
all, as CONFIG_ERRATA_SIFIVE is selected by CONFIG_SOC_SIFIVE and the
individual erratas are default-y so disabling them requires
deliberate action anyway. But for now just restore the old behaviour.

Fixes: a8e91016 ("riscv: implement module alternatives")
Reported-by: Ron Economos <re@w6rz.net>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Tested-by: Ron Economos <re@w6rz.net>
Link: https://lore.kernel.org/r/20220608120849.1695191-1-heiko@sntech.de
Cc: stable@vger.kernel.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

arch/riscv/errata/sifive/errata.c

@@ -111,6 +111,7 @@ void __init_or_module sifive_errata_patch_func(struct alt_entry *begin,
 			cpu_apply_errata |= tmp;
 		}
 	}
-	if (cpu_apply_errata != cpu_req_errata)
+	if (stage != RISCV_ALTERNATIVES_MODULE &&
+	    cpu_apply_errata != cpu_req_errata)
 		warn_miss_errata(cpu_req_errata - cpu_apply_errata);
 }