[src] Fix spelling in comments, debug messages and local variable names

Fixes in comments and debug messages:

  existance -> existence
  unecessary -> unnecessary
  occured -> occurred
  decriptor -> descriptor
  neccessary -> necessary
  addres, adress -> address
  initilize -> initialize
  sucessfully -> successfully
  paramter -> parameter
  acess -> access
  upto -> up to
  likelyhood ->likelihood
  thru -> through
  substracting -> subtracting
  lenght -> length
  isnt -> isn't
  interupt -> interrupt
  publically -> publicly (this one was not wrong, but unusual)
  recieve -> receive
  accessable -> accessible
  seperately -> separately
  pacet -> packet
  controled -> controlled
  dectect -> detect
  indicies -> indices
  extremly -> extremely
  boundry -> boundary
  usefull -> useful
  unuseable -> unusable
  auxilliary -> auxiliary
  embeded -> embedded
  enviroment -> environment
  sturcture -> structure
  complier -> compiler
  constructes -> constructs
  supress -> suppress
  intruduced -> introduced
  compatability -> compatibility
  verfication -> verification
  ths -> the
  reponse -> response

Fixes in local variable names:

  retreive -> retrieve

Most of these fixes were made using codespell.

Signed-off-by: Stefan Weil <sw@weilnetz.de>
Modified-by: Michael Brown <mcb30@ipxe.org>
Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/drivers/net/cs89x0.c

@@ -58,7 +58,7 @@ FILE_LICENCE ( GPL2_ONLY );
   Fri Nov 22 23:00:00 1996  Markus Gutschke  <gutschk@math.uni-muenster.de>
 
   * read the manuals for the CS89x0 chipsets and took note of all the
-    changes that will be neccessary in order to adapt Russel Nelson's code
+    changes that will be necessary in order to adapt Russel Nelson's code
     to the requirements of a BOOT-Prom
 
   * 6