runtime: fix incorrect comment

Fix incorrect comment for the runtime package.

Change-Id: Iab889eff0e9c622afbed959d32b8b5f0ed0bfebf
GitHub-Last-Rev: e958786
GitHub-Pull-Request: golang#57731
Reviewed-on: https://go-review.googlesource.com/c/go/+/461498
Reviewed-by: Keith Randall <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Run-TryBot: Keith Randall <[email protected]>
Auto-Submit: Keith Randall <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>
Reviewed-by: Keith Randall <[email protected]>

Author: questocat

src/runtime/mpagecache.go

@@ -21,8 +21,7 @@ type pageCache struct {
 	scav  uint64  // 64-bit bitmap representing scavenged pages (1 means scavenged)
 }
 
-// empty returns true if the pageCache has any free pages, and false
-// otherwise.
+// empty reports whether the page cache has no free pages.
 func (c *pageCache) empty() bool {
 	return c.cache == 0
 }