simplify and beautify portBYTE_ALIGNMENT (#309)

Author: mysterywolf

include/portable.h

@@ -53,29 +53,17 @@
 
 #if portBYTE_ALIGNMENT == 32
     #define portBYTE_ALIGNMENT_MASK    ( 0x001f )
-#endif
-
-#if portBYTE_ALIGNMENT == 16
+#elif portBYTE_ALIGNMENT == 16
     #define portBYTE_ALIGNMENT_MASK    ( 0x000f )
-#endif
-
-#if portBYTE_ALIGNMENT == 8
+#elif portBYTE_ALIGNMENT == 8
     #define portBYTE_ALIGNMENT_MASK    ( 0x0007 )
-#endif
-
-#if portBYTE_ALIGNMENT == 4
+#elif portBYTE_ALIGNMENT == 4
     #define portBYTE_ALIGNMENT_MASK    ( 0x0003 )
-#endif
-
-#if portBYTE_ALIGNMENT == 2
+#elif portBYTE_ALIGNMENT == 2
     #define portBYTE_ALIGNMENT_MASK    ( 0x0001 )
-#endif
-
-#if portBYTE_ALIGNMENT == 1
+#elif portBYTE_ALIGNMENT == 1
     #define portBYTE_ALIGNMENT_MASK    ( 0x0000 )
-#endif
-
-#ifndef portBYTE_ALIGNMENT_MASK
+#else
     #error "Invalid portBYTE_ALIGNMENT definition"
 #endif