clk: msm: clock-alpha-pll: Fix the workaround for the PLL_OFFREQ errata

The workaround for the PLL_OFFREQ errata was incorrectly
done - fix it by explicitly clearing the PLL_OFFREQ bit
in the disable function. The errata states that hardware
'flips' the OFFREQ bit even though SW writes the same bit
value to the same register again. Therefore, on the second
write, if SW wishes to retain the original value, SW needs
to retain the flipped bit.

Change-Id: Iaeb5c32fcc5587c5a66ef54c6491d47b27acc236
Signed-off-by: Vikram Mulukutla <markivx@codeaurora.org>