runtime: minor code style improvements (followup to change 9778049)

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/9693044

src/pkg/runtime/malloc.goc

@@ -520,7 +520,7 @@ runtime·persistentalloc(uintptr size, uintptr align)
 {
 	byte *p;
 
-	if(align) {
+	if(align != 0) {
 		if(align&(align-1))
 			runtime·throw("persistentalloc: align is now a power of 2");
 		if(align > PageSize)

src/pkg/runtime/symtab.c

@@ -563,7 +563,7 @@ runtime·symtabinit(void)
 	// Initialize tables.
 	// Memory obtained from runtime·persistentalloc() is not scanned by GC,
 	// this is fine because all pointers either point into sections of the executable
-	// or also obtained from persistentmalloc().
+	// or also obtained from persistentalloc().
 	func = runtime·persistentalloc((nfunc+1)*sizeof func[0], 0);
 	func[nfunc].entry = (uint64)etext;
 	fname = runtime·persistentalloc(nfname*sizeof fname[0], 0);