msm: mdss: update error check for dynamic fps with pp split

Currently dynamic fps configuration is checking for the
status of timing generator enable for slave controller in
the case of pingpong split. But this check will always
fail as timing generator wont be enabled for slave controller.
Remove this check to make sure dynamic fps feature works fine.

Change-Id: I097938f2b7b09a31df216c9e4879f12ed783794b
Signed-off-by: Shivaraj Shetty <shivaraj@codeaurora.org>