power: oppo: relax compiler optimizations

Unfortunately, oplus_chg is full of dangerous kernel coding practices
including weak memory orderings and will be prone to multiple breakages
if the compiler (optimization flags) changes.

Rather than spending time fixing all that, risking blowing up my phone,
relax the optimizations to -Os so that it is less susceptible to -O2/-O3
changes and follow closer to what the OPPO/OnePlus engineers originally
intended.

Change-Id: I6bc976ae6a5296ef32fc7b5e82d876138bde6465
Signed-off-by: Juhyung Park <qkrwngud825@gmail.com>
Signed-off-by: improbir <ghosh_probir@yahoo.com>