Fix broken MIPS build

Regression introduced by 9055fb408d

Fixes #104

ChangeLog.md

@@ -6,6 +6,9 @@
 1. Fixed a regression introduced by 1.5.1[7] that prevented libjpeg-turbo from
 building with Android NDK platforms prior to android-21 (5.0).
 
+2. Fixed a regression introduced by 1.5.1[1] that prevented the MIPS DSPR2 SIMD
+code in libjpeg-turbo from building.
+
 
 1.5.1
 =====

simd/jsimd_mips.c

@@ -63,6 +63,8 @@ parse_proc_cpuinfo(const char* search_string)
 LOCAL(void)
 init_simd (void)
 {
+  char *env = NULL;
+
   if (simd_support != ~0U)
     return;