checkpatch.pl: forbid strerrorname_np()

checkpatch.pl: forbid strerrorname_np()

Commit d424db2354 removed an instance of strerrorname_np() because it
was breaking building with musl libc. A recent RISC-V patch ended up
re-introducing it again by accident.

Put this function in the baddies list in checkpatch.pl to avoid this
situation again. This is what it will look like next time:

 $ ./scripts/checkpatch.pl 0001-temp-test.patch
 ERROR: use strerror() instead of strerrorname_np()
 #22: FILE: target/riscv/kvm/kvm-cpu.c:1058:
 +                         strerrorname_np(errno));

 total: 1 errors, 0 warnings, 10 lines checked

Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Michael Tokarev <mjt@tls.msk.ru>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>