MIPS: mips32/cache.S: save return address in t9 register

Synchronize the code with mips64/cache.S, in order to
allow further unifications.

Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
Cc: Daniel Schwierzeck <daniel.schwierzeck@googlemail.com>

arch/mips/cpu/mips32/cache.S

@@ -18,7 +18,7 @@
 #define CONFIG_SYS_MIPS_CACHE_MODE CONF_CM_CACHABLE_NONCOHERENT
 #endif
 
-#define RA		t8
+#define RA		t9
 
 /*
  * 16kB is the maximum size of instruction and data caches on MIPS 4K,