Fix some typos/phrasings.

doc/extending/extending_theano_gpu.txt

@@ -223,9 +223,9 @@ Here is the same kernel, but now ready to handle float16::
     """
     KERNEL void k(const ga_size n, %(type_x)s *x, %(type_y)s *y) {
         ga_size i = GID_0 * LDIM_0 + LID_0;
-        %(work_x) z = %(load_w)(x[i]);
+        %(work_x) z = %(load_x)(x[i]);
         z += 1;
-        y[i] = %(write_w)(z);
+        y[i] = %(write_y)(z);
     }
     """ % dict(dtype_x=dtype_x, dtype_y=dtype_y, work_x=work_x, load_x=load_x,
                write_y=write_y)
@@ -239,7 +239,8 @@ class property like this::
         _f16_ok = True
 
 If this attribute is not present or is False, the linker will print a
-message saying that it's refusing to use C code for float16.
+message saying that it's refusing to use C code for float16 for the
+op.
 
 A Complete Example
 ==================

theano/gpuarray/fp16_help.py

@@ -18,7 +18,7 @@ def load_w(dtype):
 
     This should be used like this::
 
-        code = '%(load_f)s(ival)' % (load_w(input_type),)
+        code = '%s(ival)' % (load_w(input_type),)
 
     """
     if dtype == 'float16':
@@ -33,7 +33,7 @@ def write_w(dtype):
 
     This should be used like this::
 
-        code = 'res = %(write_f)s(oval)' % (write_w(output_type),)
+        code = 'res = %s(oval)' % (write_w(output_type),)
 
     """
     if dtype == 'float16':