msm: acpuclock-7627: Correct the mask for disabling the pll4

The current mask for disabling the PLL4 before reprogramming
would lead to resetting the pll_enabled bitmap, which would
lead to wrong information while disabling the unused enabled PLL
at the end of the switch.

Change-Id: Id30865d2f68994d9ff4f2c0126322093763c4650
Signed-off-by: Trilok Soni <tsoni@codeaurora.org>