Fix remaining PICO_RP2350B reference (#2910)

Minor fix to #2898

Author: earlephilhower

cores/rp2040/Arduino.h

@@ -165,7 +165,7 @@ constexpr uint64_t __bitset(const int (&a)[N], size_t i = 0U) {
 #define PSRAM __attribute__((section("\".psram\"")))
 
 // General GPIO/ADC layout info
-#ifdef PICO_RP2350B
+#if defined(PICO_RP2350) && !PICO_RP2350A
 #define __GPIOCNT 48
 #define __FIRSTANALOGGPIO 40
 #else