vulkan: avoid using Float16 capability in scalar FA

Author: jeffbolznv

ggml/src/ggml-vulkan/vulkan-shaders/flash_attn.comp

@@ -137,7 +137,7 @@ ACC_TYPE perElemOpComputeSlope(const in uint32_t r, const in uint32_t c, const i
 shared FLOAT_TYPE tmpsh[gl_WorkGroupSize.x];
 shared vec4 tmpshv4[gl_WorkGroupSize.x];
 
-shared float16_t masksh[Bc][Br];
+shared float masksh[Bc][Br];
 shared vec4 Qf[Br][D / 4];
 
 void main() {
@@ -296,14 +296,14 @@ void main() {
                 uint32_t c = (idx + tid) % Bc;
                 uint32_t r = (idx + tid) / Bc;
                 if (idx + tid < Bc * Br) {
-                    masksh[c][r] = data_m[(i * Br + r) * m_stride + (j * Bc + c)];
+                    masksh[c][r] = float(data_m[(i * Br + r) * m_stride + (j * Bc + c)]);
                 }
             }
             barrier();
 
             [[unroll]] for (uint32_t c = 0; c < cols_per_thread; ++c) {
                 [[unroll]] for (uint32_t r = 0; r < Br; ++r) {
-                    float mvf = float(masksh[c * cols_per_iter + col_tid][r]);
+                    float mvf = masksh[c * cols_per_iter + col_tid][r];
 
                     Sf[r][c] += slope[r]*mvf;
                 }