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/versal/plat_psci.c b/plat/xilinx/versal/plat_psci.c
index 48d9f5f..4cf1ed1 100644
--- a/plat/xilinx/versal/plat_psci.c
+++ b/plat/xilinx/versal/plat_psci.c
@@ -36,7 +36,7 @@
 	}
 
 	proc = pm_get_proc((uint32_t)cpu_id);
-	if (!proc) {
+	if (proc == NULL) {
 		return PSCI_E_INTERN_FAIL;
 	}
 
@@ -62,7 +62,7 @@
 	uint32_t cpu_id = plat_my_core_pos();
 	const struct pm_proc *proc = pm_get_proc(cpu_id);
 
-	if (!proc) {
+	if (proc == NULL) {
 		return;
 	}
 
@@ -103,7 +103,7 @@
 	uint32_t cpu_id = plat_my_core_pos();
 	const struct pm_proc *proc = pm_get_proc(cpu_id);
 
-	if (!proc) {
+	if (proc == NULL) {
 		return;
 	}
 
@@ -201,7 +201,7 @@
 	uint32_t cpu_id = plat_my_core_pos();
 	const struct pm_proc *proc = pm_get_proc(cpu_id);
 
-	if (!proc) {
+	if (proc == NULL) {
 		return;
 	}