ARM: OMAP4: clock data: fix mult and div mask for USB_DPLL

According to OMAP4 TRM Table 3-1183, CM_CLKSEL_DPLL_USB register defines
following fields for multiplication and division factors:

DPLL_MULT (bits 19:8) DPLL multiplier factor (2 to 4095)
DPLL_DIV (bits 7:0) DPLL divider factor (0 to 255)

Acked-by: Benoit Cousson <b-cousson@ti.com>
Signed-off-by: Ameya Palande <ameya.palande@ti.com>
Signed-off-by: Paul Walmsley <paul@pwsan.com>