microblaze: Fix asm compilation warning

Microblaze ASM doesn't support hex values for mfs instructions.

/tmp/ccwiXVmt.s: Assembler messages:
/tmp/ccwiXVmt.s:19: Warning: ignoring operands: x00
Signed-off-by: Michal Simek <monstr@monstr.eu>

arch/microblaze/kernel/cpu/pvr.c

@@ -54,7 +54,7 @@ int cpu_has_pvr(void)
 	if (!(flags & PVR_MSR_BIT))
 		return 0;
 
-	get_single_pvr(0x00, pvr0);
+	get_single_pvr(0, pvr0);
 	pr_debug("%s: pvr0 is 0x%08x\n", __func__, pvr0);
 
 	if (pvr0 & PVR0_PVR_FULL_MASK)