scripts: checkpatch: diagnose uses of %pA in the C side

The `%pA` format specifier is only intended to be used from Rust.

`checkpatch.pl` already gives a warning for invalid specificers:

    WARNING: Invalid vsprintf pointer extension '%pA'

With this change, we introduce an error message with further
explanation:

    ERROR: '%pA' is only intended to be used from Rust code

Suggested-by: Kees Cook <[email protected]>
Co-developed-by: Alex Gaynor <[email protected]>
Signed-off-by: Alex Gaynor <[email protected]>
Co-developed-by: Wedson Almeida Filho <[email protected]>
Signed-off-by: Wedson Almeida Filho <[email protected]>
Signed-off-by: Miguel Ojeda <[email protected]>

Author: ojeda

scripts/checkpatch.pl

@@ -6784,6 +6784,10 @@ sub process {
 					my $stat_real = get_stat_real($linenr, $lc);
 					my $ext_type = "Invalid";
 					my $use = "";
+					if ($bad_specifier =~ /pA/) {
+						ERROR("VSPRINTF_RUST",
+							"'\%pA' is only intended to be used from Rust code\n" . "$here\n$stat_real\n");
+					}
 					if ($bad_specifier =~ /p[Ff]/) {
 						$use = " - use %pS instead";
 						$use =~ s/pS/ps/ if ($bad_specifier =~ /pf/);