Build: Fix MCUboot git tag

To be able to properly fetch a version indicated by
a tag or a commit hash move the 'v' character from the
cmake file to the value of the MCUBOOT_VERSION variable.

Change-Id: Ied87384636805205f13b1e4735e564d63417dffb
Signed-off-by: Tamas Ban <tamas.ban@arm.com>
diff --git a/config/config_default.cmake b/config/config_default.cmake
index 191fa2a..a5ca8cc 100644
--- a/config/config_default.cmake
+++ b/config/config_default.cmake
@@ -125,7 +125,7 @@
 set(CMSIS_5_PATH                        "DOWNLOAD"  CACHE PATH      "Path to CMSIS_5 (or DOWNLOAD to fetch automatically")
 
 set(MCUBOOT_PATH                        "DOWNLOAD"  CACHE PATH      "Path to MCUboot (or DOWNLOAD to fetch automatically")
-set(MCUBOOT_VERSION                     "1.6.0"     CACHE STRING    "The version of MCUboot to use")
+set(MCUBOOT_VERSION                     "v1.6.0"    CACHE STRING    "The version of MCUboot to use")
 set(TFM_INTERNAL_MCUBOOT                OFF         CACHE BOOL      "Use internal MCUboot files instead of upstream repo")
 
 set(PSA_ARCH_TESTS_PATH                 "DOWNLOAD"  CACHE PATH      "Path to PSA arch tests (or DOWNLOAD to fetch automatically")
diff --git a/lib/ext/mcuboot/CMakeLists.txt b/lib/ext/mcuboot/CMakeLists.txt
index 5fcdfd9..4c817cd 100644
--- a/lib/ext/mcuboot/CMakeLists.txt
+++ b/lib/ext/mcuboot/CMakeLists.txt
@@ -16,7 +16,7 @@
 if ("${MCUBOOT_PATH}" STREQUAL "DOWNLOAD")
     FetchContent_Declare(mcuboot
         GIT_REPOSITORY https://github.com/JuulLabs-OSS/mcuboot.git
-        GIT_TAG v${MCUBOOT_VERSION}
+        GIT_TAG ${MCUBOOT_VERSION}
         GIT_SHALLOW TRUE
         GIT_PROGRESS TRUE
         GIT_SUBMODULES ""