version: Do not make version_string[] variable as a weak

There is no platform which needs to overload version_string[] variable, so
remove weak symbol mark.

Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Tom Rini <trini@konsulko.com>
diff --git a/cmd/version.c b/cmd/version.c
index 965ac2e..2f9b898 100644
--- a/cmd/version.c
+++ b/cmd/version.c
@@ -13,7 +13,7 @@
 #include <asm/cb_sysinfo.h>
 #endif
 
-const char __weak version_string[] = U_BOOT_VERSION_STRING;
+const char version_string[] = U_BOOT_VERSION_STRING;
 
 static int do_version(struct cmd_tbl *cmdtp, int flag, int argc,
 		      char *const argv[])