clk: osm: Check for valid acd offset for input from debugfs

The user supplied acd offset is not verified to be within the acd register
range which could lead to out-of-bounds read/write. Fix the same by
checking the input and also make sure the acd base is present before the
read/write.

Change-Id: I9c0d9049d273633f6ef99593b1b45d98cc7c3827
Signed-off-by: Taniya Das <tdas@codeaurora.org>