alpha: unobfuscate _PAGE_P() definition

Way, way back it used to be
	_PAGE_NORMAL((x) | ((x & _PAGE_FOW) ? 0 : _PAGE_FOW | _PAGE_COW))
Then (in 1.3.54) _PAGE_COW had died.  Result:
	_PAGE_NORMAL((x) | ((x & _PAGE_FOW) ? 0 : _PAGE_FOW))
which is somewhat... obscure.  What it does is simply
	_PAGE_NORMAL((x) | _PAGE_FOW)
and IMO that's easier to follow.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Author: Al Viro

arch/alpha/include/asm/pgtable.h

@@ -107,7 +107,7 @@ struct vm_area_struct;
 
 #define _PAGE_NORMAL(x) __pgprot(_PAGE_VALID | __ACCESS_BITS | (x))
 
-#define _PAGE_P(x) _PAGE_NORMAL((x) | (((x) & _PAGE_FOW)?0:_PAGE_FOW))
+#define _PAGE_P(x) _PAGE_NORMAL((x) | _PAGE_FOW)
 #define _PAGE_S(x) _PAGE_NORMAL(x)
 
 /*