clk: si5341: fix reported clk_rate when output divider is 2

clk: si5341: fix reported clk_rate when output divider is 2

SI5341_OUT_CFG_RDIV_FORCE2 shall be checked first to distinguish whether
a divider for a given output is set to 2 (SI5341_OUT_CFG_RDIV_FORCE2
is set) or the output is disabled (SI5341_OUT_CFG_RDIV_FORCE2 not set,
SI5341_OUT_R_REG is set 0).
Before the change, divider set to 2 (SI5341_OUT_R_REG set to 0) was
interpreted as output is disabled.

Signed-off-by: Adam Wujek <dev_public@wujek.eu>
Link: https://lore.kernel.org/r/20211203141125.2447520-1-dev_public@wujek.eu
Reviewed-by: Robert Hancock <robert.hancock@calian.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>