Fix common misspellings

Fixes generated by 'codespell' and manually reviewed.

Signed-off-by: Lucas De Marchi <lucas.demarchi@profusion.mobi>
diff --git a/arch/mips/include/asm/paccess.h b/arch/mips/include/asm/paccess.h
index c2394f8..9ce5a1e 100644
--- a/arch/mips/include/asm/paccess.h
+++ b/arch/mips/include/asm/paccess.h
@@ -7,7 +7,7 @@
  * Copyright (C) 1999, 2000 Silicon Graphics, Inc.
  *
  * Protected memory access.  Used for everything that might take revenge
- * by sending a DBE error like accessing possibly non-existant memory or
+ * by sending a DBE error like accessing possibly non-existent memory or
  * devices.
  */
 #ifndef _ASM_PACCESS_H