Remove wrongly repeated words in comments

Clean up misrepetitions ('if if', 'the the' etc) found throughout the
comments. This has been done manually, after grepping
case-insensitively for duplicate if, is, the, then, do, for, an,
plus a few other typos corrected in fly-by

v2:
    * proper commit message and non-joke title;
    * replace two 'as is' followed by 'is' to 'as-is'.
v3:
    * 'a integer' => 'an integer' and similar (originally spotted by
      Jason Ekstrand, I fixed a few other similar ones while at it)

Signed-off-by: Giuseppe Bilotta <giuseppe.bilotta@gmail.com>
Reviewed-by: Chad Versace <chad.versace@intel.com>

src/compiler/nir/nir.h

@@ -804,7 +804,7 @@ typedef struct {
 } nir_deref_var;
 
 /* This enum describes how the array is referenced.  If the deref is
- * direct then the base_offset is used.  If the deref is indirect then then
+ * direct then the base_offset is used.  If the deref is indirect then
  * offset is given by base_offset + indirect.  If the deref is a wildcard
  * then the deref refers to all of the elements of the array at the same
  * time.  Wildcard dereferences are only ever allowed in copy_var