Back out an error introduced with commit 02c33f66c5a8be774034cd40e4125e9323c7b4d8. Causes an infinite loop in up_lowputc(). From Max Neklyudov.

arch/arm/src/sam34/sam_lowputc.c

@@ -299,6 +299,8 @@ void up_lowputc(char ch)
           /* Send the character */
 
           putreg32((uint32_t)ch, SAM_CONSOLE_BASE + SAM_UART_THR_OFFSET);
+          irqrestore(flags);
+          return;
         }
 
       irqrestore(flags);