cmake: arm: fix ARMFVP_FLAGS for ns variant

Support to run non secure variants with ARMFVP was enabled with
a7122cf5 and fa45bebc
however, the pattern search doesn't work as expected.
This commit fixes that.

Signed-off-by: Sudan Landge <sudan.landge@arm.com>

cmake/emu/armfvp.cmake

@@ -1,4 +1,4 @@
-# Copyright (c) 2021-2022 Arm Limited (or its affiliates). All rights reserved.
+# Copyright (c) 2021-2022, 2025 Arm Limited (or its affiliates). All rights reserved.
 # SPDX-License-Identifier: Apache-2.0
 
 find_program(
@@ -53,7 +53,7 @@ elseif(CONFIG_ARMV8_A_NS)
     --data cluster0.cpu0="${APPLICATION_BINARY_DIR}/zephyr/${KERNEL_BIN_NAME}"@0x88000000
     )
 else()
-  string(FIND "${ARMFVP_FLAGS}" " -a " ARMFVP_APPARG_POS)
+  string(FIND "${ARMFVP_FLAGS}" "-a;" ARMFVP_APPARG_POS)
   if(${ARMFVP_APPARG_POS} EQUAL -1)
     set(ARMFVP_FLAGS ${ARMFVP_FLAGS}
       -a ${APPLICATION_BINARY_DIR}/zephyr/${KERNEL_ELF_NAME}