target: catch dap_lookup read error

Issue found by clang-3.1

Change-Id: I2e922ec83117e75db5bec1e82edaa75a9e6e7464
Signed-off-by: Spencer Oliver <spen@spen-soft.co.uk>
Reviewed-on: http://openocd.zylin.com/778
Tested-by: jenkins
Reviewed-by: Freddie Chopin <freddie.chopin@gmail.com>

src/target/arm_adi_v5.c

@@ -1265,6 +1265,8 @@ int dap_lookup_cs_component(struct adiv5_dap *dap, int ap,
 			retval = mem_ap_read_atomic_u32(dap,
 					(component_base & 0xfffff000) | 0xfcc,
 					&devtype);
+			if (retval != ERROR_OK)
+				return retval;
 			if ((devtype & 0xff) == type) {
 				*addr = component_base;
 				retval = ERROR_OK;