Add missing space in linker script

Author: deepikabhavnani

targets/TARGET_Freescale/TARGET_KLXX/TARGET_KL25Z/device/TOOLCHAIN_GCC_ARM/MKL25Z4.ld

@@ -147,7 +147,7 @@ SECTIONS
         __end__ = .;
         end = __end__;
         *(.heap*)
-        .= ORIGIN(RAM) + LENGTH(RAM) - STACK_SIZE;
+        . = ORIGIN(RAM) + LENGTH(RAM) - STACK_SIZE;
         __HeapLimit = .;
     } > RAM