Precision fix for inversesqrt.
Precision fix for inversesqrt.

Fixes all dEQP failures in inversesqrt and normalize.

Change-Id: Ifd1ac2714fa95bab1c720b65c95a27bbf23ea933
Reviewed-on: https://swiftshader-review.googlesource.com/13728
Tested-by: Alexis Hétu <1c7141772178a7e80858c3db5052b328076f08f4@google.com>
Reviewed-by: Nicolas Capens <51edc787c30f24c4904e8ffbb5523c3a9f7a451d@google.com>

google/swiftshader,bkaradzic/SwiftShader,bkaradzic/SwiftShader,bkaradzic/SwiftShader,google/swiftshader,bkaradzic/SwiftShader,google/swiftshader,bkaradzic/SwiftShader