Remove warning: vehicle RecurrentTimer_test.cpp

0xdeadbeef is exactly 32 bits, so it is interpretted as an unsigned
integer which was causing a warning. Since it's a test value, I changed
it to 0xdead which is interpretted as a signed integer.

Test: pass
Change-Id: Ibb75b23461700d77158e2337b8a472e87629ad61