msm: sde: format fix for XRGB1555 type formats

Update the condition check which sets the bit to inform hardware that
there should be an alpha component in the rotator's destination
format.  The previous check failed for RGB formats containing a 1-bit
alpha value.

Change-Id: Ib326e07ff513431323e10a8c0592e0a164b72dca
Signed-off-by: Steve Cohen <cohens@codeaurora.org>