fexc: Fix thinko in script decompiler

Both the error output in function decompile_section() and the
definition of GPIO_BANK_MAX in script.h suffered from an "off
by one" logic. The bank numbering in the .bin is based on 1,
so it should be added to ('A' - 1) for human-readable output,
and the maximum number corresponding to 'N' is 14.

This became apparent when trying to translate a fex2bin-compiled
a80_optimus_board.bin back to its original .fex equivalent.
Signed-off-by: Bernhard Nortmann <bernhard.nortmann@web.de>

script.h

@@ -19,7 +19,7 @@
 
 #include "list.h"
 
-#define GPIO_BANK_MAX	13 /* N */
+#define GPIO_BANK_MAX	14 /* N, (zero-based) index 13 */
 
 /** head of the data tree */
 struct script {

script_bin.c

@@ -269,9 +269,12 @@ static int decompile_section(void *bin, size_t bin_size,
 			} else if (gpio->port == 0xffff) {
 				; /* port:power */
 			} else if (gpio->port < 1 || gpio->port > GPIO_BANK_MAX) {
-				pr_err("%s: %s.%s: unknown GPIO port bank %c (%u)\n",
-				       filename, section->name, entry->name,
-				       'A'+gpio->port, gpio->port);
+				pr_err("%s: %s.%s: unknown GPIO port bank ",
+				       filename, section->name, entry->name);
+				char c = 'A' + gpio->port - 1;
+				if (c >= 'A' && c <= 'Z')
+					pr_err("%c ", c);
+				pr_err("(%u)\n", gpio->port);
 				goto failure;
 			}
 			v[0] = gpio->mul_sel;