msm: clock-debug: Replace ULONG_MAX with INT_MAX for 'fmax' assignment

The 'fmax' variable is an integer, not an unsigned long. Use the
correct macro so that the comparisons of 'rate' and 'fmax' works
correctly. Now, doing a 'cat list_rates' for a clock without voltage
constraints prints a non-empty list.

Change-Id: Ie93894e3d026115c2671980d8520eb8fb09d5e49
Signed-off-by: Matt Wagantall <mattw@codeaurora.org>