libocl: Consider only bottom ilogb(2m-1)+1 bits
libocl: Consider only bottom ilogb(2m-1)+1 bits

Signed-off-by: Jan Vesely <6a2ac3bd1a50b5b4969c0b358741eeb258bebe0c@gmail.com>
Reviewed-by: Ruiling Song <286a174c1339c6eff91abc41c3a1012c95030c95@intel.com>

wdv4758h/beignet,wdv4758h/beignet,wdv4758h/beignet,wdv4758h/beignet,wdv4758h/beignet