ASoC: fsl-ssi: fix do_div build warning in fsl_ssi_set_bclk()

do_div() requires that the first parameter is a 64-bit integer,
which but clkrate was defined as an unsigned long.  This caused
the following warnings:

 CC      sound/soc/fsl/fsl_ssi.o
sound/soc/fsl/fsl_ssi.c: In function 'fsl_ssi_set_bclk':
sound/soc/fsl/fsl_ssi.c:593:3: warning: comparison of distinct pointer types lacks a cast
sound/soc/fsl/fsl_ssi.c:593:3: warning: right shift count >= width of type
sound/soc/fsl/fsl_ssi.c:593:3: warning: passing argument 1 of '__div64_32' from incompatible pointer type
include/asm-generic/div64.h:35:17: note: expected 'uint64_t *' but argument is of type 'long unsigned int *'

Signed-off-by: Timur Tabi <timur@tabi.org>
Signed-off-by: Mark Brown <broonie@linaro.org>