fix(plat/xilinx/versal): resolve misra R10.3

MISRA Violation: MISRA-C:2012 R.10.3
- The value of an expression shall not be assigned to an object with a
  narrower essential type or of a different essential type category

Signed-off-by: Abhyuday Godhasara <abhyuday.godhasara@xilinx.com>
Change-Id: I9c6dd8dba40db8067b46947ceff295732648612a
diff --git a/plat/xilinx/versal/plat_psci.c b/plat/xilinx/versal/plat_psci.c
index e7bf8f8..1f3b2bf 100644
--- a/plat/xilinx/versal/plat_psci.c
+++ b/plat/xilinx/versal/plat_psci.c
@@ -193,7 +193,7 @@
 {
 	VERBOSE("%s: power_state: 0x%x\n", __func__, power_state);
 
-	int pstate = psci_get_pstate_type(power_state);
+	unsigned int pstate = psci_get_pstate_type(power_state);
 
 	assert(req_state);