microblaze: Fix systems with MSR=0

u-boot BSP generates XILINX_USE_MSR_INSTR macro
even for system with MSR=0. That's why explicitly
check that MSR=1.

Signed-off-by: Michal Simek <monstr@monstr.eu>

arch/microblaze/include/asm/asm.h

@@ -62,7 +62,7 @@
 #define NOP	__asm__ __volatile__ ("nop");
 
 /* use machine status registe USE_MSR_REG */
-#ifdef XILINX_USE_MSR_INSTR
+#if XILINX_USE_MSR_INSTR == 1
 #define MSRSET(val) \
 	__asm__ __volatile__ ("msrset r0," #val );