Cosmetic: Fix a number of typos, no functional changes.

Fix various misspellings of things like "environment", "kernel",
"default" and "volatile", and throw in a couple grammar fixes.

Signed-off-by: Robert P. J. Day <rpjday@crashcourse.ca>
diff --git a/post/board/lwmon5/sysmon.c b/post/board/lwmon5/sysmon.c
index da37d66..cca1a26 100644
--- a/post/board/lwmon5/sysmon.c
+++ b/post/board/lwmon5/sysmon.c
@@ -22,7 +22,7 @@
  *
  * LCD backlight is not enabled if temperature values are not within
  * allowed ranges (-30 .. + 80). The brightness of backlite can be
- * controlled by setting "brightness" enviroment variable. Default value is 50%
+ * controlled by setting "brightness" environment variable. Default value is 50%
  *
  * See the list of all parameters in the sysmon_table below
  */