disp: msm: sde: set bounds on debugfs core perf input

Previously debugfs nodes for fix_core_ab_vote, fix_core_clk_rate,
and fix_core_ib_vote could be set to any value. This change
will compare fixed values to userspace values and set it to the
maximum of the two to avoid crashes with invalid input.

Change-Id: Iae89279eb1effe3daf8cd0aef5acceb55992ab03
Signed-off-by: Samantha Tran <samtran@codeaurora.org>