clk: si5351: expand compatible strings in documentation

checkpatch.pl doesn't know how to expand "silabs,si5351{a,a-msop,b,c}"
and so generates warnings about si5351-compatible devices appearing to
be un-documented. Resolve this by documenting the compatible options
supported by the clk-si5351 driver individually.

Signed-off-by: Brandon Streiff <[e-mail]>
Acked-by: Stephen Boyd <[e-mail]>
Signed-off-by: Rob Herring <[e-mail]>

Documentation/devicetree/bindings/clock/silabs,si5351.txt

···
 ==I2C device node==
 
 Required properties:
-- compatible: shall be one of "silabs,si5351{a,a-msop,b,c}".
+- compatible: shall be one of the following:
+	"silabs,si5351a" - Si5351a, QFN20 package
+	"silabs,si5351a-msop" - Si5351a, MSOP10 package
+	"silabs,si5351b" - Si5351b, QFN20 package
+	"silabs,si5351c" - Si5351c, QFN20 package
 - reg: i2c device address, shall be 0x60 or 0x61.
 - #clock-cells: from common clock binding; shall be set to 1.
 - clocks: from common clock binding; list of parent clock