vmx_tests: Silence warning from Clang

Clang complains:

x86/vmx_tests.c:8429:40: error: converting the result of '<<' to a boolean
 always evaluates to true [-Werror,-Wtautological-constant-compare]
         vmx_preemption_timer_zero_inject_db(1 << DB_VECTOR);
                                               ^

Looking at the code, the "1 << DB_VECTOR" is done within the function
vmx_preemption_timer_zero_inject_db() indeed:

	vmcs_write(EXC_BITMAP, intercept_db ? 1 << DB_VECTOR : 0);

... so using "true" as parameter for the function should be appropriate
here.

Message-Id: <20200514192626.9950-11-thuth@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>