Fix missing DECLARE_GLOBAL_DATA_PTR on CONFIG_LPC2292 in serial

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>

cpu/arm720t/serial.c

@@ -125,6 +125,8 @@ serial_puts (const char *s)
 
 #elif defined(CONFIG_LPC2292)
 
+DECLARE_GLOBAL_DATA_PTR;
+
 #include <asm/arch/hardware.h>
 
 void serial_setbrg (void)