[committed] MIPS/GAS: Update `match_const_int' description

[Maciej W. Rozycki]

Remove a stale reference to FALLBACK parameter from the description of 
`match_const_int', matching commit 1a00e61226b3 ("Remove soft_match"), 
<https://sourceware.org/ml/binutils/2013-08/msg00133.html>.

	gas/
	* config/tc-mips.c (match_const_int): Update description.
---
binutils-mips-gas-match-const-int-fallback.diff
Index: binutils/gas/config/tc-mips.c
===================================================================
--- binutils.orig/gas/config/tc-mips.c	2017-05-12 08:45:42.000000000 +0100
+++ binutils/gas/config/tc-mips.c	2017-05-12 08:47:14.978493693 +0100
@@ -4841,8 +4841,7 @@ match_expression (struct mips_arg_info *
 
 /* Try to get a constant expression from the next tokens in ARG.  Consume
    the tokens and return return true on success, storing the constant value
-   in *VALUE.  Use FALLBACK as the value if the match succeeded with an
-   error.  */
+   in *VALUE.  */
 
 static bfd_boolean
 match_const_int (struct mips_arg_info *arg, offsetT *value)