timer: xtensa_sys: Cleanup use of C99 types

We introduced some see C99 types, so convert them over to the Zephyr
types.

Signed-off-by: Kumar Gala <kumar.gala@linaro.org>
diff --git a/drivers/timer/xtensa_sys_timer.c b/drivers/timer/xtensa_sys_timer.c
index aeaed81..e35a23a 100644
--- a/drivers/timer/xtensa_sys_timer.c
+++ b/drivers/timer/xtensa_sys_timer.c
@@ -41,7 +41,7 @@
 #define GET_TIMER_CURRENT_TIME(void) XT_RSR_CCOUNT()
 
 #define XTENSA_RSR(sr) \
-	({uint32_t v; \
+	({u32_t v; \
 	 __asm__ volatile ("rsr." #sr " %0" : "=a"(v)); \
 	 v; })
 #define XTENSA_WSR(sr, v) \