fix(xilinx): follow MISRA-C standards for condition check

As per the MISRA-C standards, there should be proc == NULL not just
!proc.

Fix the same.

Change-Id: I0e7650c09b045882a0235869d7ef9fca27f96d9a
Signed-off-by: Ronak Jain <ronak.jain@amd.com>
diff --git a/plat/xilinx/zynqmp/plat_psci.c b/plat/xilinx/zynqmp/plat_psci.c
index 9fd00db..1e7df05 100644
--- a/plat/xilinx/zynqmp/plat_psci.c
+++ b/plat/xilinx/zynqmp/plat_psci.c
@@ -44,7 +44,7 @@
 	}
 
 	proc = pm_get_proc(cpu_id);
-	if (!proc) {
+	if (proc == NULL) {
 		return PSCI_E_INTERN_FAIL;
 	}
 
@@ -68,7 +68,7 @@
 	uint32_t cpu_id = plat_my_core_pos();
 	const struct pm_proc *proc = pm_get_proc(cpu_id);
 
-	if (!proc) {
+	if (proc == NULL) {
 		return;
 	}
 
@@ -97,7 +97,7 @@
 	uint32_t cpu_id = plat_my_core_pos();
 	const struct pm_proc *proc = pm_get_proc(cpu_id);
 
-	if (!proc) {
+	if (proc == NULL) {
 		return;
 	}
 
@@ -133,7 +133,7 @@
 	uint32_t cpu_id = plat_my_core_pos();
 	const struct pm_proc *proc = pm_get_proc(cpu_id);
 
-	if (!proc) {
+	if (proc == NULL) {
 		return;
 	}