Update little-to-big endian GetSwapFloat functions

rSt >> pPtr[3] >> pPtr[2] >> pPtr[1] >> pPtr[0] results in error:
  no match for 'operator>>' in 'rSt >> *(pPtr + 3u)'

Change-Id: I1820bac8c72f7633ab01a17bf5d073b988e1b58c
Reviewed-on: https://gerrit.libreoffice.org/8207
Tested-by: Michael Stahl <mstahl@redhat.com>
Reviewed-by: Michael Stahl <mstahl@redhat.com>