pru: Use a pointer when working with send_data array items

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

src/pru/internal.h

@@ -22,15 +22,16 @@
 #define ALT_PRU_PTR(ptr) ((typeof(ptr))((uint32_t)(ptr) ^ 0x2000))
 
 // Layout of shared memory
+struct shared_response_buffer {
+    uint32_t count;
+    char data[64];
+};
 struct shared_mem {
     uint32_t signal;
     const struct command_parser *next_command;
     uint32_t next_command_args[16];
     uint32_t send_push_pos, send_pop_pos;
-    struct {
-        uint32_t count;
-        char data[64];
-    } send_data[4];
+    struct shared_response_buffer send_data[4];
     const struct command_parser *command_index;
     uint32_t command_index_size;
     const struct command_parser *shutdown_handler;