linux-user: fix microblaze get_sp_from_cpustate()

get_sigframe() uses regs[1] and this is actual SP.

Signed-off-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <20180409115212.875-1-laurent@vivier.eu>

linux-user/microblaze/target_signal.h

@@ -23,7 +23,7 @@ typedef struct target_sigaltstack {
 
 static inline abi_ulong get_sp_from_cpustate(CPUMBState *state)
 {
-    return state->regs[14];
+    return state->regs[1];
 }