msm: camera: isp: Replace unsafe bitwise operations

Using addition and substraction for bitwise operations is unsafe and
error prone. If some of operations are repeated, the mask can be
leaved in invalid state. Also, cleaning of masks relies upon stats
composite IRQ register, which value is invalid in case of preceeding
VFE hw reset. This fix uses bitwise AND and OR for mask operations and
cleans properly the mask irrespectively of VFE condition.

Change-Id: Iad4f7e18b10589de5c227babe89acecdd85fb885
Signed-off-by: Petar Sivenov <psiven@codeaurora.org>