mx6: crm_regs: Fix MXC_CCM_CIMR_MASK_PERIPH2_CLK_SEL_LOADED

According to the Reference Manual the 'mask_periph2_clk_sel_loaded' field of
register CCM_CIMR corresponds to bit 19 so fix its definition accordingly.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>