Fix floating-point luminance/alpha pixel upload.
Fix floating-point luminance/alpha pixel upload.

We were expecting R or RG internal formats, instead of L, A, or LA.

Change-Id: I6ee145341819460dda262b017db6d8105860f49a
Reviewed-on: https://swiftshader-review.googlesource.com/17508
Tested-by: Nicolas Capens <51edc787c30f24c4904e8ffbb5523c3a9f7a451d@google.com>
Reviewed-by: Alexis Hétu <1c7141772178a7e80858c3db5052b328076f08f4@google.com>

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