msm: mdss: Remove backlight min level checks during backlight scaling

There is currently a check to prevent backlight scaling when the backlight
level is below the minimum level. This min level and scale are both sent by
userspace. There should be no check in driver comparing backlight to min
level when doing scaling. That check will be done in user mode. The
driver should have the flexibility to do scaling in all scenarios.

CRs-Fixed: 1090387
Change-Id: I6b036db5169c89091ca452c68d6773d9df6d5e06
Signed-off-by: Benet Clark <benetc@codeaurora.org>