tracing: doc: fix "for a while" typo

Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/xygdnynf7m55p7d27ovzqtdjaa7pua3bxuk5c22cnmoovaji5e@tarta.nabijaczleweli.xyz

Author: nabijaczleweli

Documentation/trace/histogram.rst

@@ -249,7 +249,7 @@ Extended error information
   table, it should keep a running total of the number of bytes
   requested by that call_site.
 
-  We'll let it run for awhile and then dump the contents of the 'hist'
+  We'll let it run for a while and then dump the contents of the 'hist'
   file in the kmalloc event's subdirectory (for readability, a number
   of entries have been omitted)::