net/mlx4_en: Prevent potential integer overflow calculating Hz

net/mlx4_en: Prevent potential integer overflow calculating Hz

The "freq" variable is in terms of MHz and "max_val_cycles" is in terms
of Hz.  The fact that "max_val_cycles" is a u64 suggests that support
for high frequency is intended but the "freq_khz * 1000" would overflow
the u32 type if we went above 4GHz.  Use unsigned long long type for the
mutliplication to prevent that.

Fixes: 31c128b66e5b ("net/mlx4_en: Choose time-stamping shift value according to HW frequency")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/aDbFHe19juIJKjsb@stanley.mountain
Signed-off-by: Paolo Abeni <pabeni@redhat.com>