mm/Kconfig: fix spelling mistake "whats" -> "what's"

There is a spelling mistake in the Kconfig help text. Fix it.

Link: https://lkml.kernel.org/r/20201217172717.58203-1-colin.king@canonical.comSigned-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/Kconfig

@@ -713,7 +713,7 @@ config ZSMALLOC_STAT
 	select DEBUG_FS
 	help
 	  This option enables code in the zsmalloc to collect various
-	  statistics about whats happening in zsmalloc and exports that
+	  statistics about what's happening in zsmalloc and exports that
 	  information to userspace via debugfs.
 	  If unsure, say N.