cpu: fix dec_16

When getting the register index, an incorrect shift was being
used. Fix the test case by correcting this.

Signed-off-by: Max Regan <mgregan2@gmail.com>

src/apps/cpu_integ_test.c

@@ -77,7 +77,6 @@ static void test_dec(const void *test_data)
 	g_assert_cmpint(lr35902_get_reg_8(&cpu, LR35902_REG_H), ==, 0);
 
 	g_assert_cmpint(lr35902_get_reg_16(&cpu, LR35902_REG_DE), ==, 0xffff);
-
 	
 	free(src);
 }