Use scalar_mode in expand_shift_1

Use scalar_mode in expand_shift_1

Since this function handles scalar and vector shifts:

  machine_mode scalar_mode = mode;
  if (VECTOR_MODE_P (mode))
    scalar_mode = GET_MODE_INNER (mode);

is equivalent to:

  scalar_mode = GET_MODE_INNER (mode);

2017-10-23  Richard Sandiford  <richard.sandiford@linaro.org>
	    Alan Hayward  <alan.hayward@arm.com>
	    David Sherwood  <david.sherwood@arm.com>

gcc/
	* expmed.c (expand_shift_1): Use scalar_mode for scalar_mode.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@253999 138bc75d-0d04-0410-961f-82ee72b054a4