i2c: qup: use proper type fro clk_freq

It is used with of_property_read_u32(), so it should be u32.

Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Acked-by: Bjorn Andersson <bjorn.andersson@sonymobile.com>
Fixes: 10c5a842 ('i2c: qup: New bus driver for the Qualcomm QUP I2C controller')