simplify and beautify portBYTE_ALIGNMENT (#309)

diff --git a/include/portable.h b/include/portable.h
index 3768e2c..774d3b5 100644
--- a/include/portable.h
+++ b/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